3/32' v 1/8' ?

Do you mean your wheel is all the way in, rather than tension? If you go up by 1 tooth on the freewheel you won't need much extra room so you may not need a new chain.
I also doubt you would have any chainline issues as freewheels must be fairly similar?
And one last point, why don't you just buy another 1/8 freewheel (could even try a Dicta one so it is exactly the same?

1) yeah, the wheel is all the way in into the dropouts, no more room to adjust tension.
2) I dunno anything about frewheel similarities, my guess is more tooths = bigger size wheel = less tension needed? or am i wrong?
3) that can be done, only if I find a good quality freewheel. also I wanted at least a couple more tooths to even up the uphills (lisbon has plenty of those, y'know).