Help with new drain/vent/waste system

I'm currently building my own house (HEAVY into DIY!) and have a few DVW questions. Mostly, I'm having trouble trying to figure out where to put clean-outs. According to the books, you should have one on the high end of every horizontal run. That will be a lot of clean-outs! What about areas where it's hard to fit one in? I have a 3" run draining two toilets that I would like to run through the floor joists. The problem comes with the clean-out. They call for 18" of clearance for a 3" clean-out, but the joists are only 16" apart. Can I drill a hole in the next joist for access? Theoretically, it's more than 18" clearance, but you'd have to bend the snake up between the joists. I'm not sure if an inspector would buy that. The only other option for this run would be to drop the 3" run below the joists- something I'd rather not do with an eye to finishing the basement someday.

The next issue is 3 fixtures in close proximity- a washing machine standpipe, a lavatory, and a shower. According to the charts, that's too much for a 2" drain. Should I combine them into a single 3" pipe, or run two separate 2" pipes?

Lastly- Does it matter whether a vent is 'upstream' or 'downstream' of a fixture? For example, I want to put the vent for a toilet in the wall behind it. This is 15" downstream, towards the main drain. It would be nearly impossible to place it upstream of the toilet. I don't think it matters, but can't find any reference to this.

Any help on these questions would be most appreciated. This all looked easy at first, but is quickly becoming complex. Our local inspectors aren't very helpful (or strict) but I want it to function well. Thanks!