Always an interesting subject: what should be your first lathe? Art Ransom is right on the money when he says to find a club first. Then start asking questions and visit people's workshops to see their lathes. If you are in a hurry or are determined to go it alone, you have a couple choices on your overall plan.
Plan 1: Buy a small but solid mini or midi to start learning on, and plan on adding a bigger lathe when you are ready, but expect to keep the small lathe. It's handier than you might think to have two lathes, for many reasons I won't go into here. Find one with a 1 1/4 x 8 spindle with #2 morse taper if you can so your accessories will fit your bigger lathe when you get it.
Plan 2: Buy whatever appeals to you right now and expect to trade up in a couple years if you really enjoy turning. Again, look for a 1 1/4 x 8 spindle so you can keep your accessaries when you upgrade. Don't be swayed by features over quality. Look for massive construction more than anything. You don't want to face the common beginner quandry of not knowing if a problem is you or your lathe. The same is true for Plan 1 - mass equals happiness.
Plan 3: Bite the bullet and spend a ton of money for a lathe you won't outgrow. The risk here is that you don't know at this point what aspect of turning will become your main passion in years to come. Even the best lathes have their pro's and con's, so you may end up with one that is really not well suited for your purpose.
Drive systems are always a trade off on lathes costing less than at least a couple thousand dollars. Single speed motors with several pulley speeds give you the most power and smoothness for your money, they tend to be trouble free, and they can often be replaced with a bigger motor if you want. Variable pulley systems tend to be noisier and vibrate more, and you may have maintenance problems, but the convenience is nice if you are an impatient type who will be irritated by having to change pulleys to change speeds. Variable pulleys usually won't go any slower than a standard pulley system. I think probably most standard pulley lathes can be adapted with a simple clutch mechanism for very slow speeds and soft starts (see Del Stubbs' bowl video). You can't do that with a variable pulley system (or a rotating headstock). Electonic variable speed is a joy if you get one with enough power for roughing out at low speed, but you've got to spend the big bucks to get one that's adequate. Art and I both have 2 hp Powermatic 3520's, which is the cheapest lathe I have seen with excellent electonic variable speed. The smaller 1.5 hp electronic variable speed lathes are a compromise - you pay less but you may feel underpowered at times. Remember, electronic variable speed lathes lose power at lower rpms, so you need a lot to start with. Variable pulley systems and standard pulleys keep the motor working at full power when you gear down.
Power at very low rpms is not needed for slow speed sanding and finishing, but it's relatively simple to build a separate device for this with a couple bearings and a shaft threaded to match your lathe spindle. Add a cheap motor and pulleys to get you down in the rpm range you want. A good scrounger can come up with all this for free or nearly so at scrap metal yards or plumbing or heating contractors. Unless you know the right person you'll have to pay the machinist to thread the shaft.
Since you mentioned rotating headstocks, I will tell you my experience with this. I have had two lathes with that feature and it is very nice for hollowing out hollow forms and not much else. If you have a short bed lathe, you can work from the end, but a long bed can get in the way for hollowing, especially wider-than-tall shapes, unless you are using a captive bar system like the Jamieson. You don't need a rotating headstock for spindle work, and it really isn't that important for bowls. Don't be mislead by advertising which suggests you can turn really big if you rotate the headstock. Most machines are sized pretty well over the bed for their true capacity. They really aren't capable of more if you rotate the headstock, and you lose tailstock support as well. The exception would be shallow objects without a lot of mass, like platters or picture frames, but you may find yourself underpowered and overgeared if you attempt large diameters on a basically small lathe.
I guess that should give you plenty to think about before making your first lathe purchase. I hope I haven't confused the issue even more. Best wishes, turning is great fun.
-mike paulson, fort collins, co