Shim and boost questions + afr

[Gunnar]

My supra is being delivered on monday, i got one with a metal head gasket and arp bolts installed, needs a new paintjob but the mechanical side of the thing is realy good.

Now, i got me the 550cc injectors, lexus afm, afr meter and extra boostgauge.
With the standard turbo and those mods how many shims or what boost should i go for?

Then the afr meter i got doesn't have a probe, it just says in the manual that the green wire goes to the o2 sensor. If i hook this up with a split cable to the wire that goes from the ecu to the o2 sensor won't i screw up my signal due to parallel resistance values?