IIRC a change on the boxster is 9.5qts so buy more
There is an approved oil list for all new cars. Can easily find it on the web. M1 0w-40 is what I use. Def NOT the 15-50 I run the in the old 911. There are only a few synthetics you can find in the states that are on the list. (funny, but both the boxster and tt list the oil weights & capacity in the manual)
Only one drain & cartridge/insert filter on the early engines. No clue what the 997.2s do. Make sure you have a wrench to get it off. The orange universal one I have doesn't work worth a darn. I bought the special VW/audi one for less than the porsche one and it fits like a glove. The housing has an odd # of facets I think.
There are cabin air filters & engine air filter. Not sure which you're referring to.
box/996 don't have a service indicator light so I don't know. If a durametric tool can turn it off (which it should) I can help you out.