When a project only gets bigger and bigger

You are not alone.
There is alot of good advice in this thread for sure.
Work on the things that are absolutly needed to get done to get the car on the road again first then you can get stuck with the things that are on the list of things that are just nice to have done.
On days with very limited amounts of time,try to just get something done anyway even if its a small thing,it all adds up over time and keep your workarea somewhat tidy it helps alot.
This is from someone that has a duster that has been parked and riped apart for way to long,partialy due to me trying to do things in the right order and therefore not being able to get anything done at all.
I wish you the best of luck,just keep at it,you will get there over time just try to avoid ripping the whole car apart and get stuck.