Sorry to hear about your issues
On the high revs at startup: I believe the slip is maintained until the fluid temperature is 25C, so it will do it at an ambient of 15.
I would really not try anything other than the exact Volvo fluid (except maybe Toyota as I believe they use the same gearbox so would have the same fluid) - I think that can only introduce more unknowns and make things worse.
Are there any fault codes for the gearbox? You probably need a proper VIDA equipped garage to check.