Don't adjust the wastegate with washers, you limit the amount the wastegate is able to open and increase the risk of creeping or clogging. Google "grainger boost controller" and build a cheap, manual boost controller yourself.
Yes, your ignition timing may be off. If you don't know how to check and set the timing you should look at the thread in the MKIII FAQ section.
As for the trouble with the cold starts I'd start with diagnosing the cold start injector circuit.
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