Where for a tube-newb to start?

I don't get what you are saying. If you already have the amp, why do you need reviews?

Here is a resource that, if you really want to understand what you are getting into, you should find helpful: (http://www.buildtubeamps.com/tubeampbooks.html)

It's too bad Glass Audio is no longer in print. I loved that magazine. Anyway; it's been incorporated into another, that can be found here, along with a some other resources: (http://www.nutshellhifi.com/Linkstxt.html)

If your question is what is the characteristic sound of particular brand/year tubes in each of these tube categories, there's lot's of anecotal info on the web if you simply run a search using the tube type. I have 'rolled' various tubes in different equipment over the years, and it is an enjoyable aspect of the hobby that can make a noticeable difference in sound.
Recognize that for any given tube, it may yield different results depending on how it is used in the circuit; thus, one person may 'like' a particular tube in a piece of gear that, to you, in your gear, may sound too euphonic.
Also worth noting that unless you are really knowledgeable, there is much confusing info about the old tubes- apparently, different companies shared manufacturing facilties, so a tube legitimately branded under a well-known name and place of origin may have actually been made for them by another company in another country. It is worth dealing with a legitimate supplier- there are several- if you are going to delve into 'new old stock' since the price of some old, highly sought after tubes is considerable and the potential for fakery is there.

Read the descriptions of stuff that "thetubestore.com" sells. It's laid out reasonably (unlike a lot of other dealers) and clearly. Good stuff, and a nice company to buy from.