Retirement is a state of mid - It's taken me about 6 years to get to the stage of not working - so don't expect an instant change.
re the cars - serious or not it's your choice!
Now you will have more time (or so you might think!)
A newer SL is not so much of a DIY project as a dealer project.
An older SL ( Pre 89) can be more home maintained (no so much tech stuff) as a newer one
My thoughts:
Get a new runabout for day to day driving ( or you may already have one)
Repace the 129 with a 107 or even an earlier one
spend a year doing ALLLLLL the bits you are worried about
Enjoy life
Cheers
Jim