You don't know if you are afoot or horseback. This is a hard pass. You are looking at a swapped car (which is ALWAYS a partial birth abortion) and then looking ahead to putting a 6 speed from a current car into a future car. You are sixteen steps down the road. Every engine and every trans will fit into every Subaru firstly. Secondly, all swaps...engine or trans require research that YOU have to do. There's no copy/paste answer and we have an entire Conversions Forum forum here for this.
You are buying a neverending project. If you are OK with this, buy the damn thing and leave us alone. Return when you have specific questions. Holistically, you should NOT buy they damn thing as its broken now and you are scheming as to how to take your good Subaru and cobrifabbing it into this new one to create a FrankenSubaru that will be a greater version of each of the two cars. That will likely not happen.