I forgot you have more cars than time to drive them at this point
DannyP good point on the pan vs frame.
Engine choice, if you want to use a stock ECU, you are limited in years ie 2008 ish more or less, small car has a list of what years are available with the stock ECU but you can also use a Subarugears digital gadget but I have no experience or recommendation with that one.
I think Carey has a good program getting used cars and a new Short block with stock ECU. IMO.