Welcome to the Team Sam!
One word in your post disturbs me; "investment". You should buy your car to enjoy, to drive, to share with family and friends. You should never buy an old used car thinking you are going to make money by doing so. I will tell you right now you will loose every dime you put into it.
For an example consider the clunker you bought for $5,000. You work to get it mechanically sound enough to be able to drive it to the body shop for another $5,000. Now you will have three to five years to make more money to pay someone $17,000 to $25,000 to repair all rust damage and install new wiring. So five years after you bought it you can now take it to the upholstery shop to have the interior repaired but you will need another $3,000-$7,000 and you have to pay up front just to wait another six months. But after words you are the proud owner of a shiny new used car that is worth maybe $10,000 to $15,000 at best and if you doubt me just try and sell one.