As others mentioned, you did not say how old/how many miles the car has. The clutch/RMS job on itself is $1000-$1500. Almost certain at one stage you will have an issue with the MAF, another $200-$300 right there.
Honestly I would save some of that for maintenance.
I am actually doing the opposite you are, bringing the car back to as stock as possible from whatever the previous owner did. The factory options they got (short shifter, body kit, etc) I am keeping but everything else is going away (intake with cone filter, etc).
And as said, the best mod you can get for a Boxster for $5K is to buy a newer Boxster S.
Whereabouts are you in Canada? I am in Ottawa.
CR