Unless you're running a free zine, most of your decisions should start and end with the budget in mind. There is a cost associated with every decision you make.
When budgeting, your breakeven amount is how much it will cost to give your contributors a full bundle free of charge, shipping included. Have some money set aside in case you need to cover expenses that your sales might not, and in all honesty, unless you and your team cannot cover the breakeven amount then you should reconsider your ability to commit to the project.
To best manage your budget, you can either try to control the costs or make decisions that are ultimately going to generate revenues. Profitability is ultimately finding that sweet spot between a lean project that is still marketable enough to generate sales. Projects with high sales may end up with low profits simply because of the high cost of merch items included, bundles priced too low, and the profit needing to be split between 60+ contributors. But even a project that doesn't reach 100 sales can still end up with decent per-contributor shares if there were few/cheap merch options and a smaller number of contributors. So think about how each of your decisions will affect what your contributors will get in the end.
(Of course, marketability isn't always everything -- if it's a niche topic you feel absolutely passionate about, go make it! But be realistic about how much it might sell, and lower your costs accordingly.)
Zine specs
Contributor numbers
Merchandise offerings
Shipping
Fandom size and activity
Market saturation / competition
Theme appeal
Value proposition
Make a copy of this template and remove/add additional rows and columns as needed.
This is a two-part template I use to manage zine budgets. The first part (Cols A-K) I use primarily for planning bundle pricing and costs. For me, it's a good visual to see how much the production cost of each bundle really is, so that I can price accordingly. As a general rule of thumb, your bundle price should be at least 3x the cost of your merch. But you are balancing your profitability with the marketability of your pricing. Zine buyers are used to buying zines at $25-50. If this puts your bundle price at a very high cost, consider dropping merch items instead! And once preorders begin, I use the first part of the template to track sales per bundle.
The second part I use for the actual budget, as well as to track budgeted vs actual revenues and expenses once things start rolling in. This is more bigger picture and helps identify all the "hidden costs/expenses" in your budgeting phase, like ordering a few extras of things for replacements, contingency shipping, and shipping the items from suppliers over to your shipping person's place.