Disc Rotor / Lockring Play

[Mike L]

Hi! Many apologies for my state of panic, but a friendly commenter on Reddit (/r/bikewrench specifically) suggested that I cross-post my question here to see if anyone here could help, so please forgive the rough copy-paste-edit job from my original post there.

Basically... with the pandemic going on I recently got a nice custom gravel wheelset built for me using White Industries CLD hubs, which I've spent the past couple days assembling but have now run into some problems, particularly as I stubbornly insisted on pairing them with Campy H11 disc rotors and thus had to source my own lockrings for them.

One of these I think I have down, but I could really use help on the other two!

1. Front lockring fit over endcap (not too bad + will be solved, I think): Going in, I had been warned about this issue, but for some reason thought it was the rear when it was in fact the front where a lockring tool wouldn't fit between an internally-splined lockring and the end cap; I have a bottom bracket tool and 6-bolt to centerlock adapter (for the thin externally-splined lockring that it comes with) on order to solve this
2. Rear lockring gap with rotor (stuck here, please help!): After tightening my lockring to 40Nm (and maybe a little bit past -- saw some thin metal strips come out, oops), there still seems to be a 1-2mm gap where the rotor can move between the hub and the lockring; did I order too thin a lockring, should I use a cassette spacer (or rotor shim), or am I doing something wrong?
3. Stripped rear caliper bolt (not fatal for now, but what do I do?!): I actually discovered the play in the rotor when test-mounting the wheel to see if I'd need shims, so initially I thought I'd loosen the flat-mount caliper mounting to do a routine re-centering as it seemed the new rotor was more outboard than my old wheelset's; I guess my bike came with one of these bolts already super tight and I ended up stripping the hex head with just a run-of-the-mill L-shaped allen key 😣... so newbie question, what do I do now so that I could re-center my rear brake in the future?
   

I was super excited to get these wheels but now I'm a little flustered as to how to get them to a rideable state, so I really, really appreciate any help I can get on them! Thanks so much in advance!