Re: Too short?
It's certainly easier and much less intimidating to start on a bike that fits you comfortably. I don't think it's necessary to be able to flatfoot a bike (I've never owned one that I could do that with) but it really helps, as a beginner, to be able to put the balls of both feet down solidly. Something else to consider is that Monsters are relatively heavy for their size, and it's not going to be easy to pick the bike up when you drop it. I say when rather than if because I've never known a short rider who didn't drop the bike a few times. I still do it occasionally, after 12 years.
I'd recommend getting a bike that is low enough without a lot of modification, even if it's something you don't like much, and gaining experience and confidence before getting a Monster. Once you've had some practice, and have learned some specialized techniques for riding a bike that's taller than you are, it's not hard to do. But added onto trying to master the basics of riding, it's a huge challenge.
You might consider something like a Yamaha XT225 or TW200 to start with; they're both small and light. As long as you don't trash the bike, you should be able to sell it and recoup most of what you paid for it.
"Without a safety net you're freed<br />To find serene pleasure in speed"