This is what I'd do, in order of preference:
1. Nothing. This costs a lot of time and money, because "nothing" means maintaining the car with authentic Subaru parts according to the manual. "Nothing" is also a prerequisite for any/all changes you want to do.
2. Up pipe. No tune needed, but you will have to fix the CEL with a resistor.
3. Down pipe. Tune needed.
I would not bother doing a down pipe alone, and I would not do the intake under any circumstances here.
This means I'd not do a down pipe without the up pipe, and I'd not do the down pipe without a tune. The tune goes with the down pipe, if you ignore the intake. Since you should forget about the intake, down pipe --> tune.
I would do an up pipe without a tune though.