I think you find the GOSM to be a pretty decent smoker without doing any mods, and should give years of reasonably trouble-free service.
Hmm, 6 butts might be crowding it a bit. I like to keep a few inches of space between the food and the smoke chamber walls, as the outside runs hotter. I think if you go one grate position down from the top with 2 butts, then another 2 on the bottom grate should work like a charm. That will leave enough head-space above each pair for even flow of heat through the smoke chamber. The butts will shrink their foot-print as they cook, buy also get taller, and can easily touch and start to lift the grate above them if you don't use double-spaced grates....been there once. OK, now, that was with the butts laying flat...if they would stay standing on edge, you might be able to hold 3 per grate, but that's iffy.
For wood chips, I recall using about 1/2 full box, heaped-up and lid on...dry chips, not soaked...3-5 hours smoke. Small chunks smoke longer. The wider smoker with more meat may not smoke quite as long as mine did due to needing hotter burner setting, just so you have an idea on time.
Water pan should be checked after first 3 hours, refilled, then you can estmate how long before it runs dry. Temp spikes may indicate dry water pan.
Oh, speaking of temps, the door therm cannot be trusted until it's been calibrated (7/16" hex on on thermo stem)...normal for every smoker I've ever used. A probe in the middle of the grate between the butts will suffice.