I say start with what you can afford. I fortunately didn't have to spend much time at the lower levels because I had someone stake me. It was the best thing that ever happened to me, I started making some decent money right away (instead of winning $2-$3 per session).

I would suggest that you deposit a couple hundred more in your account and move up to NL25. But only if you can handle it (meaning you're not taking money away from rent and that you'd be "okay" losing this money even though you most likely never will if you keep reading this site).