 Re: help choosing a manual 4-colour press
I would recommend buying used. You save a lot (my 6 colour press is 3500$ new and I paid 1200$)
Things will be off - platen arms will be less flush with the screen arms, threads will be worn, bearings may need replacing.
If you are looking to do this seriously and continue doing it, I would go with a rotary, floor model press, and I would look for a used 6 colour.
Micro registration allows you to make fine adjustments to your screens after you have clamped them into the press. There are essentially two plates on each screen arm.
You would clamp your screen into one, and the other one is attached to the press. They are clamped together, and when you register your screens you can loosen the outer plate, adjust it with threaded guides. You turn them and the plate that your screen is attached to moves in or out or side to side. These are standard micros, usually called XY micros.
If you are anal about registration, these are a must. I haven't ever used the joystick registration. It's cheaper and I've heard once you've used it for a while it's fairly easy, but not quite as easy as regular XY.
The only complaint I've heard with it, is if you move the registration a certain way and decide that you've gone too far, there is no way to return to where you were before, whereas with a regular head you could just thread it back to where it was. That's just what I've heard, might not even be true.
I bought a used Caps press and would recommend them. Micros aren't the fastest (I've only compared to M&R) but once you get the job locked in, it holds tight registration.
See the attached picture for a visual on how micros work. | 
