Go V8 then turbo it... Its take a lot of time and money to pull a lot of power from The 4 bangger. But it is a hell of a lot of fun. Money is better spent with a good v8.
Do your home work. www.turbomustangs.com
The turbo swap is much easier. To start you will need to move your fuel lines from the left side to the right side, a lot more rewiring in the harness and if you have AC you will need the hoses and may need the condenser from the donor car. If you don't have a complete donor car, running around trying to round up the parts would be enough for most people to give up.