National Park and OTS Access - Most national parks open at 8:00 am. and close at either 4 or 5 pm. and cost 10-20 dollars (usually dollar currency is fine). Many are closed on Mondays. However, Palo Verde and La Selva are official OTS designations and were open on Monday last time I checked. Carara National Park was also open on a Monday on my last visit.
Most birding guides are not allowed to enter national parks before their official opening times.
Wildlife refuges and local parks are a bit less predictable in their hours. You may be able to get in a park before or after hours, but there are no hard rules about that. I've gone into to several national parks and refuges before anyone arrived to take my money as an admission fee, then paid on the way out. It's never been a problem yet. When in doubt, play it safe and only stay within the appropriate 8-4 time frame. Check ahead if possible.
There's a more peculiar price structure for touring La Selva OTS. Entrance fee structures can be found here.
Weather can be a problem any time of year, so I wouldn't let the summer wet season deter me if I really wanted to bird on my own in summer. The months of May through early August are wetter months but not dramatically wet. We're not talking monsoon season. Usually one gets afternoon or evening rains at that time.
The summer wet season has some definite peculiarities. Seasonal rainfall by month is sometimes quite different in each geographic area of Costa Rica during this season. Many tour companies like to say that there is a "little summer" in July when rainfall is less than it is during the surrounding months of June and August. The tourist industry loves using this factoid. Unfortunately this is not altogether true on the Caribbean side of the country and in southern Costa Rica. Statistical measurements show that July is frequently the wettest month in parts of the Caribbean lowlands and on the Osa Peninsula (although most mornings are generally rain free). Guanacaste and some of the central mountains, on the other hand, do show substantially less rainfall in July than the surrounding summer months. In essence, I take the "little summer" story with a grain of salt. Avoid making plans in September and October if it can be helped (unless you are exclusively birding the Caribbean coastal areas which are slightly dryer than the rest of Costa Rica during those months). Outside of that, I wouldn't worry about it.
Internet Access - WiFi Internet access in much of Costa Rica is generally available in most hotel lobbies or resort restaurants. Recently we have noticed several places now offer wireless Internet access in the hotel rooms. It's not blazingly fast and is not perfectly reliable every day, but most people with laptops use it successfully and are happy it's available. My perception is that wireless access continues to be upgraded every year.
Span Bridges - Span Bridges are bridges where one is allowed to walk leisurely, sometimes at high elevations through the canopy, and observe wildlife. There are productive span bridges at Monteverde, Arenal, and Heliconias Lodge. These bridges are occasionally very productive for birdwatching. However, bridges like these move a bit when people walk on them. I went to the Arenal Hanging Bridges twice early in the morning with mixed results. People walking on the bridge made birdwatching difficult. It's like trying to bird from a raft in open ocean. I was finally told to bird on the bridges in the afternoon after the tour groups left - around 2:00 PM. This was much better. I like the span bridges a lot in general, but it is really feast or famine. One may need to visit multiple times to reap the benefit. And if it's not completely obvious, span bridges are not zip lines. No sane person birds from a zip line.
Cell Phone Service - Trying to explain cell phone service in Costa Rica hurts my brain just thinking about it. However, the Real Costa Rica - cell phones web site has a very good summary of the current issues - but even then it's still confusing. All the U.S. providers like ATT and Sprint handle international calling a little differently if you're bringing your cell phone.
For the record, a phone with texting capability can be handy. ATT in the United States, for example, can arrange an inexpensive international texting plan just for the time you are on vacation (assuming ATT is your provider). As iPhone users, my wife and I pay a small fee to ATT for 50 outgoing text messages. Incoming text messages are free. I use my smart-phone email system only when there is WiFi access at a hotel or restaurant (tons of places have free WiFi). I turn off "data roaming" on my phone and I turn my phone completely off much of the time - which can cut down on random incoming phone calls. Then I can turn my phone on once or twice a day and get messages. If someone needs to talk to me by phone instead of by email or text, they can email or text me first about the subject so I can see if it's critical. International texting is more forgiving in this system and much cheaper. But all cell phone provider services are not the same. Talk to your cell phone provider about your phone\email\Internet options. And be sure and tell close friends NOT to call you for the time you're gone.
The more devices that can be left at home, the better... in my opinion.
Tipping - Most bills in Costa Rica related to wait-services often include a 10% gratuity in the price of your meal. Check all restaurant bills for this. Nevertheless, I always tip, sometimes generously. I make sure I'm tipping at least 10% on top of the established 10% already taken out. One place birders might not know to tip is when the car is parked temporarily to bird somewhere or to leave a car to walk into a crowded roadside restaurant. There are frequently guys standing around in restaurant parking lots or elsewhere who do nothing but watch your car while you're away from it. One will eventually run across these guys as they will usually have some kind of orange or off-color jacket on. This is not really a scam. They actually do you a service. Remember, birders frequently leave valuables in the car - binoculars, passports, luggage, etc. So not only do I tip these guys, but I tip them BEFORE I walk to my destination. I want them to see me and my car, and I want them to know I'll be generous if they protect my car from some petty theft.
Drivers usually get tipped about $3 a day if they just drive. Every so often, I get a driver who doubles as a fairly good bird guide. On some tours, they sometimes accompany the actual paid bird guide. It's almost like getting a guide-and-a-half. In this case, I have to adjust to something like $5 a day or more. I've actually had a driver who had over 700 birds on his Costa Rica list.
Bird guides almost always get a good tip. I'm usually at my happiest after a day with a bird guide. For a longer tour, I usually tip guides at least $10 a day. For just a single day of guiding, I usually tip much more depending on how invested the guide is in showing me specific birds. Sometimes tipping seems never-ending, but I just budget it into cost of the trip. In my opinion, the tipping of guides is an essential part of the natural history tourist industry. Tourism may be big in Costa Rica, but the guides themselves aren't making a significant amount of money on their services. Good bird guides are ready to start birding at 5:30 AM, and they sometimes work well into the night with owls. They cart around scopes, field guides, and playback mechanisms. Most of guides I've been with worked long and hard to get people to see birds. I know what most bird guides in Costa Rica charge for their service. Adequate compensation should include a tip.