I've been using these from Amazon: 300 for $14

https://www.amazon.com/gp/product/B07KJ9H31P/ref=ppx\_yo\_dt\_b\_search\_asin\_title?ie=UTF8&psc=1

These are the ones I got that fit really well: https://www.amazon.com/dp/B07KJ9H31P?ref=ppx_pop_mob_ap_share

Basically I just put a little hot glue on the bottom of the base and then stick the magnet in while it's cooling! It's been really quick and I don't get super glue all over my fingers.

Here is my personal breakdown:

I made wood painting handles with magnets inset in them via the design from Goobertown Hobbies YouTube channel, and I super glue a single 6x2mm magnet these to the base of each single trooper unit. This is plenty strong for painting and storage. (I use really useful boxes brand and installed thin metal sheeting so the troops stick right down. No rattle. It's great)

To answer your more delicate question, I magnetized the guns on my At-RTs with SUPER TINY ones. I think they were 2x2mm.

Best advice I can supply is watch YouTube videos and find what other creatives have done and pay CLOSE attention to the polarity of the magnets. You don't want to screw up the polarity, lol.