Plan on use a walbro 255 fuel pump and megasqurit 2, as it is cheaper and I've built one before. No it will not hurt anything if you don't run a o2 sensor, just set the EGO step size to 0%. With MS the o2 only provides feedback for EGO correction. Most people running MS in their cars do not run o2 sensor, but they run wideband O2 sensor to a gauge not to the MS. As for different elevations MS 2 has a built in MAP for that, as for temps run a IAT and a temp sensor if you want.