How much weight can my roof rack handle over my Jeep Gladiator?

It depends on your rack system and where it's attaching to. But the quick answer is over 150 lbs wen the vehicle is in motion.

Should I get a drill or non drill roof rack for my Jeep Gladiator?

You're welcome to read the section about this topic above. It depends on your needs when it comes to weight capacity, and if you're handy with power tools.

What can I carry over my Jeep Gladiator roof rack?

Depends on the rack and weight capacity, but from kayaks, to skis, luggage, and roof top tents.

Should I get a platform rack, a half rack or crossbars for my Gladiator?

Crossbars are great for boards or kayaks, full platform racks for larger and heavy items, and half racks allow you to easily remove the freedom panels.