Keep the springs you have now, to start. I would go 35 wt. in front, 40-45 wt. in back.

Just get a non-rebuildable 27T for right now, run that, save bucks, and get something like a XeRun or EZRun system. They are very inexpensive for brushless systems, and from what I'm seeing, very good quality. Get a pinion that is 4 to 6T larger than what you have now.

That should get you started.