Questions from a Tube Preamp newbie

@aberyclark , there's no rule that says that all four tubes need to be the same type. When I owned a Perseus Magnum, I had 2 RCA Blackplates in the front Gain position, and Mullards as Cathode Followers. The RCA's provided open, dynamic sonics, while the Mullards provided warmth and classic tube bloom.

The best deal that I've come across is the Brimar CV4003 at Upscale. These are British tubes with warmth, but have more extension than Mullard at the top and low-end.

I wouldn't use the term sparkle to describe the Brimars, I would say they have a nice amount of "air" in the highs, a very realistic sound. 
RCA Cleartops and Amperex have sparkle, meaning extended highs. Never tried JJs.

Yes, using a different tube type as cathode follower gives you an almost endless variation of sonics. Rogue responds very well to tube rolling and  there are many different 12AU7's.

I have NOS Mullards ECC 82’s , sounds like somebody threw a blanket over my system . Kinda like pushing the Dolby button on a cassette player .

As always, YMMV.
Regarding Mullard and other NOS brands, if they are noise-tested they should sound good for many hours. There are several types of Mullards; longplates, shortplates, ladder plates, with square getter or with halo getter. ECC82 labelled "Made in Great Britain" are of the highest build-quality.

There is a "house sound" to these tubes, warmth with a relaxed top-end (since they are British they should be called valves).
1950’s ECC82 longplate square getters present open and warm sonics with rich textures; I own several pairs. The CV4003 is a military-spec boxplate with a wide soundstage, and to my ears, sound more "lively," whereas the short plate sounds more "closed-in."

Philips tubes made in the UK factory will have the same sonic signature as Mullard. Phillips Holland was the parent company of Mullard and Amperex.