The normal reccommendation seems to be start with 4x5. That's great if you want to shoot with 4x5. My girl friend on the other hand just started shooting large format, started with 5x7 and loves it. She finds the larger ground glass much easier to compose and focus, plus her interest is in contact printing not enlarging. So given the op's interest in contact printing and alternative processes 4x5 might not be the best way to go.
Roger
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