Epilogs are generally decent machines, although they can be horrendously expensive if parts fail on them. I had an Epilog at work which managed to fry its mainboard, as well as its Y axis encoder - the mainboard was (IIRC) several hundred pounds to replace, and the Y axis mtoor assembly had tobe swapped out, because Epilog's UK reps wouldn't do parts support to that granular a level.
With regards to things fitting up the stairs don't forget that you can take the legs/base off, and just turn it 90 degrees, so the front is facing down. That's how I got my 700*500 laser up two flights of stairs at home - all you need is a willing participant to provide an extra pair of hands.
Having worked with both RF and CO2 lasers, I've not noticed there to be a world-shattering difference in terms of quality and speed, if you're careful with job setup and are using decent control software (at least, not at the desktop/office-sized end of the market). Out of the box, RF lasers are a bit faster/more controllable, but it's nothing that can't be worked around - the only real tangible advantage is the frequency control, but that can largely be accounted for in speed and power settings anyway.
I'm going to sound like a bit of a shill, but Lightburn is a package that replaces the horrible Chinese software that comes with most cheaper laser cuters, and I personally think it at the very least brings it up to the level of Epilog's software, if not supercedes it. The only thing about an Epilog that I like over my Chinese laser now is that it runs with a closed-loop motion system. I've not had step loss at any point with my machine, but it'd be nice to never have to even think about it as a possibility . I may try to retrofit a closed-loop motion system at some point anyway, if the RuiDa controller has the capacity to deal with it.
The Epilog certainly sounds like a good deal, but I maintain that dropping 5 grand in one sitting is a lot of money - if you can achieve similar results with a glass tube laser that costs 25% as much, it might be a more sensible initial investment.