Budget? That's the first thing to think of. Do you want just a muffler, or a full catback? Those rely on budget as well.
Also, you may want to wait until you get to Cali, because if you get one that drones heavy or with a sound you don't like, you're stuck with it for the drive across the country.
I have a Corsa DB, love it, the sound, the zero drone, the quality, everything. I have been starting my truck while standing outside most of the time ever since I got it, just to hear that first rumble... Not cheap, so if you can't go that route, understandable.
Also, weld it in for sure. Clamps can be used, but they inevitably will fail or need tightening. Easier to remove, but if you do it right and get what you want on the first go, welded in is the best option.
