In order...
Yes. Probably. Yes.
Arguably the preamp contributes most to the overall performance of the amplifier, assuming the power amplifier is not hopelessly mis-matched with the loudspeakers (this is unlikely with Cerwin Vegas - although they need power to grip those bass units, they are sensitive and the minimum impedance is benign enough to make them easy to drive with almost any amplifier). I don't necessarily subscribe to the 'straight wire with gain' argument suggesting all power amps basically sound the same, but the preamplifier is the part where the wheels are most likely to come off the wagon in the whole amplifier bit. The same applies in the preamplifier stage within an integrated amplifier, but usually these have the advantage of working with a known and fixed power amplifier section also within the integrated amp, so the two are designed in tandem and designed to work well together.
There are some excellent pre-power combinations recommended in this thread, but some of them seem to be a touch out of band, given the kind of budget you are pointing toward. Albarry, Art Audio and Tron are fine UK made products, but including both preamp and power amps will be pushing you toward a considerable investment beyond that budget, especially in the latter case. I think you might still be better off with a good integrated amplifier as you originally suggested, under the circumstances.
I also think that, despite the antipathy toward retailers endemic to many forums, your best bet at this stage is to have a couple of professional demonstrations of UK made integrated amplifiers within your budget. If you are unable to obtain a home demonstration, ideally bring your own speakers and your music to the store's demonstration listening room to replicate the amp/speaker interaction. If this is impossible, you can usually 'listen through' some pretty substantial differences in system, because if one amplifier sounds intrinsically 'right' to you, chances are that would apply more universally than many here would care to admit.
From experience, try to limit the number of products you audition - if you listen to five different amplifiers in relatively quick succession and still feel you haven't found the right one, you are probably expecting too much from the whole experience, and it becomes increasingly unlikely that subsequent amplifiers thrown into the mix will hit the spot. It's all too easy to fall victim to the tyranny of choice at this point.
However, the most important thing to take along is an open mind. If you listen to a few amplifiers and conclude that the one you like is the one everybody on a forum hates, screw 'em. They don't have to live with your choice... you do. They don't have your room, your system, your ears... you do. People in audio often have strong opinions coupled with very long memories - their like or dislike toward the products of a manufacturer may be swayed by an event that took place decades ago (even the Great Train Robbers only got 30 years), and you should not let such things cloud your judgment.