it's up to you..you need the tacho..i would definitly get the boost also..as for the rest..your going to be using your existing cluster arn't you? if your temp gauge work with the sender..use it..other wise..get a temp gauge..the only thing that will work no worries is the speedo (providing you get the right speedo drive) and the fuel..oil pressure is good..but if your not going to use it why bother? i don't know if that will confuse you
tacho - depends..5" monster around the $250 (basic model w/ shift light)
all the other gauges depending on what size you get them and where..ie boost, temp, press, amps, fuel, are about $80 each.. depending on where you go..
good brands are autometer (der!) i prolly would stay away from the 'supercheap' 3 in a row cluster combos if you want it done properly..