Options 2 and 3 are almost in direct opposition to each other. MF is great for the detail you get, but long lenses in MF are still very expensive, and fast, long lenses are almost non-existant. To get the equivalent functionality in 645 as you'd get from the Canon 200/2.8, you'll probably have to sell your soul (along with the souls of some loved ones). I'll take the difference in these two options as a sign that you're looking for something to satisfy you, rather than something for a specific professional purpose.

If I was in your shoes and had $600 to spend, I'd move on to option 4: A used Mamiya RB67 system. You can pick up an RB Pro-S, 120 back, waist level finder, and 127mm C lens for under $400 from KEH in Bargain grade. (If you wait a few weeks you'll probably find the same system with the 90mm lens at the same price; they just seem to be out of that configuration right now.)

Admitedly, the RB isn't as easy to carry as a 645 system, but it isn't horrible either. You can use the system hand-held if you want to, but if it's detail in landscape that you're looking for then you want the biggest negatives you can get with good glass in front of them, all locked down on a good tripod. The RB is a great system for this. Plus, with the bellows built in, it's a decent macro system out of the box. For this price you don't get a light meter, but there are a lot of choices out there for less than the $200 you'd have left. (Igorcamera.com has a Soligar Zone VI modified spotmeter for $135...if ever there was a sleeper in light meters, this is it. Easy to use, easy to read, and very accurate...plus it takes regular 9V batteries. Mine's served me very well.)

Don't be afraid of KEH's "Bargain" grade. They have a reasonable return policy, and the RB system I bought from them last year in bargain condition showed only wear around the back of the body and front of the film back; the rest of the camera was in amazing condition and has worked flawlessly from the day I got it. (KEH's Excellent, Excellent Plus, etc. grades are for collectors more than for users.)

For detail in landscapes, nothing beats a bigger negative with good glass.