360 or 270?
If you're going to do swappable panels anyway, you could make one of each.
Whichever one you pick, you're going to see a bunch of games that you'd love to play, and can't.
Shifters... High/Low? High low with a trigger? Actual gears?
Again, if you're looking for a one-size-fits-all solution, you're not going to find it.
You might consider going completely modular, and being able to swap shifters/wheels at will.
A 4-speed gated shifter, like the ones used on Cruisin', etc... will allow you to play most of the games, but isn't perfect for all.
Pedals? 1 or 2 pedals?
This one depends on what games you intend to play, and what your playing style is.
I can get by with only an analog gas pedal for most arcade games.
For sim games I do use the brake pedal alot.
Is it better to go with the arcade wheels like seen on ultimarc or go with a Microsoft one? I had one before and it seemed to require alot of work to calibrate each game. Just curious.
For 360 games, an arcade wheel is really the only choice.
For 270 arcade games, a good quality wheel, like those that Happ's makes is great, but they are fully playable with a PC wheel as well.
For PC games, I would highly recommend the Logitech Driving Force Pro, or G25.
Logitech's Force Feedback makes the experience for me, and I wouldn't settle for anything less.