All great advice so far, and I agree with pretty much all of it. Technique and diet are probably going to be the two biggest factors for the reasons flipcollar stated. Technique can buy you a bunch of weight straight off the bat, and getting lighter will mean you need to pull less to get 2x bw.
With the training, 5/3/1 is a good option. I'd be almost tempted to suggest the Coan-Phillippi program, but I'd be very cautious about that if you're not at least an intermediate. I mean, I love deadlifting and I think my DL is respectable enough for my bodyweight but I myself would have to think very carefully before doing it. I still reckon you should look at the program, though. I know that kind of contradicts what I just said, but if you look at it and think, wow, that's JUST what I want, have a go. You could even run two Coan cycles for a 35 kg/75 lb increase each cycle. That'd be 150 lbs over 20 weeks, which I think is reasonable.
Definitely don't neglect squat training, and front squats are one of the best DL assistance exercises around IMO, especially when paused at the bottom for heavier loads (doing these after DLs worked well for me). Pull-ups too, and while they will royally suck to do at your weight, your grip will improve a bunch from doing them. Even hanging from the bar will help. Heavy dumbbell rows/Kroc rows have recently helped me a ton too.
Absolutely squat and DL on different days. If you want to do extra DL work, do a variation after squats. I had some success using snatch grip DL after squats.
Whether you pull sumo or conventional, the above advice from everyone applies.