Bankrolling and moving up the limits

I started playing not too long ago, and have found that I have a knack for the game, at least I am doing OK so far. I played a couple NL-Holdem tournaments with co-workers, and was hooked. Wanting to play more, but not having any card rooms in my area I moved to the play money tables. That got boring after a couple of months, and I just went to Party a little over a week ago. I put up $100, and after a week of playing the NL25 Tables I am over $200(Including the 20% they released to me after 100 hands).

I have heard that the NL50 tables are pretty tough but NL100 and NL200 are a little easier, is that true?

I have 400 BB in my bankroll for NL50. Is that good enough for a tougher set of tables? Or should I sit tight until I have $300 and move up to the NL100's? Is only a week(approximately 30 hours of play) too short a time to make such a decision?

Any and all advice, and/or abuse, is welcome.