That is great the slippage is fixed, though it’s concerning to hear that you (and PeterG I think it was) had to modify the bearing caps so they could clamp the bearings sufficiently before the clamps hit the frame. Maybe something has changed a little with the newer frames?
Hard to say how often you need to check the bolts as imo there is a lot to be said for not messing around with the hub once things have settled down, limiting the chance to strip, round out crank bolts etc. Fwiw I check mine every four-six weeks or so now, but initially it was weekly, then fortnightly.
Like other guys I use blue loctite on both the bearing cap bolts and crank bolts - NOT the shift buttons though. Using loctite esp on the crank bolts is mentioned in the hub manual and discussed in a few threads e.g. Setup thread. It seems to be the trick when it comes to keeping the crank bolts tight, limiting the need to check them too often.
Important tip when tightening crank bolts - it’s mentioned in the Schlumpf manual but worth repeating to minimize the chance of rounding out/stripping the inside of the crank bolts:
Push the shifting shaft inwards using the Allen wrench to make sure that the wrench engages properly (fully).
Gotta do that, but even then I wish the crank tightening mechanism/process was a LOT more robust so you could check it whenever, swap cranks etc without worrying about damaging the crank bolts. Oh yeah, it’s a good idea to have a spare pair of crank bolts including buttons, just in case.