I used 5mm spacers on my gti and measured threads etc. Standard bolts are just enough with 5mm spacer

Can I ask does the same apply to adaptors? I'm fitting some Porsche teledial's to mine when they turn up with adaptors I have three sets 15mm, 20m and 25mm. Will I need extended bolts?
You will need longer adapter bolts yes, but standard wheel bolts.
The adapter bolts are a bit specialised and should come with the adaptors. Make sure you ask.
As said find out what type of bolt you need for the porsche wheels (radius or taper) but you only need standard length