I'm running ADK TL > R4 and I'm satisfied with it. I've made some nice tapes with it.
I wouldn't recommend putting a UA-5 in the mix unless you were looking at an oade or busman modified unit. I ran a digi-mod UA-5 before I got the R4 and IMO an digi-mod UA-5 would be a decrease in quality. There are a lot of good pre-amp options besides the V3. If you are willing to buy used there are a lot of nice options that are $300-500 less than a v3. Check out the lunatech v2, PSP2, Sonosax SX-M2, Sound Devices MixPre, and Apogee MiniMe. If you want spend upwards of $1k you could consider the V3, neve portico, m148 or m248, etc...
IMO a lunatech V2 is a better match for the R4 than the V3 if you plan on running 4 channels pretty regularly, because when running 4 channels on the R-4 they must all be analog. SO when running 4 channel you'd have to run analog out on the v3. If you aren't going to be using the A/D of the V3 then it's really not worth the extra $300-400 you'd have to pay.