What is the right size bike for me...

I wouldn't worry much about the starting - I'm 5'4 and on an RM125.

The height problem becomes more of an issue on MX starts and on off-camber sections in the woods.

Start by filling in the rest of this:

Try to include the following info in your first post
1) your physical size (both height and weight are important)
2) How physical / aggressive are you ?
3) what do you plan to ride- MX/SX tracks, woods, fields with friends or ?????
4) Do you have any riding experience?
5) Do you think you will race ?
6) Are you mechanically inclined and will you be doing your own bike work?
7) Do YOU have a preferance to a brand/ motor choice (2 or 4 stroke)?
8) Do you have a dealer close by your home that you might use and what brand(s) does he carry?
9) How much do you plan to spend on a bike?
10) anything else that you think would help form an opinion

That said, the problem for you is that you want to do tracks and trails.

Most trail bikes totally suck on a track - the suspension is not nearly as good as an MX bike.

I'm 140-150 lbs depending on the time of year. ;)

I love 125s - although I had mine bored to 144cc.

A lot of guys here like the 250f MX 4 strokes, but they're more maintenance and more money to keep running. They are easier to ride than a 125 2 stroke, though, because they're about the same size, only a little heavier, and have a lot more low end power.

Still, I like the 125s.

My bro is 160 pounds and he prefers a 250 2 stroke - but not so much because of the extra power - he likes the extra weight - it makes the bike feel more stable to him. And since he does a lot of woods riding, the 250 2 stroke is easier to "lug" around than a 125.

My .02 worth . . .

Sounds to me that you want a trail bike. from what I've read I would look into a ktm 200xc

like you said a crf250x would be good for you.

Either a 250 fourstroke or 200 two-stroke would fit you perfectly. I motocross my EC200 from time to time and for my skill level it is just fine on the track. Offroad I have the best bike, hands down. I raced a mud race on the weekend and was one of the only bikes to not get stuck on slippery hill climbs and mud holes. The other two bikes that made it look easy were GasGas 300s. Yesterday I raced a dry, fast, rocky whooped out course and my bike performed equally well. I think a 200 two-stroke is the perfect size bike for lighter riders. By the way, I'm 6', 155lbs.

Oh, robwbright, height is a huge issue in the woods, anytime. Get on some tight switchbacks or windy hills and being able to put a foot down easily can make a huge difference.