Can the digger remain outside?

Yes, they are powder coated and can withstand the elements.

Can I bolt it down?

Yes, simply drill holes in the baseplate to secure using bolts or anchors. It is recommended that you use black rustoleum or something similar to spray the holes before fastening to anchors.

Is there a weight limit?

Not really, they are constructed of strong metal and professional welds. Adults and kids alike can enjoy these diggers.