If it’s not broken or missing pieces you can 100% put it back, you might need to slightly force open the latch on the PCI if the tolerance is too tight

Epomaker TH80 or any Keychron keyboard that you like for your budget.

As for mice, go to Rocket Jump Ninja’s top mice list and take your pick, you won’t go wrong. If anything I’d recommend to stick to hand size and for personal preference I always recommend to avoid ambidextrous mice because they’re not as comfortable but that could be just me…