Hi,
The SSL 8000 GB, probably is one of the best SSL consoles every made in my opinion. Specially if you consider modern workflows.
I think TR is something you can retrofit on a later stage, although in my opinion is something you definitely want to have on these consoles nowadays. Just make sure you have a fully working computer with it, since this is the most problematic and Achilles knee of the entire console, with parts getting very expensive and hard/impossible to fix.
For the total recap of the console, if you're going to do it yourself, save a couple thousand of bucks for the materials. The 8000 GB is not that old, when comparing with an E or earlier G is. Try to know if it was ever recapped, and if it was when it was. Capacitor life on an SSL 4/5/6/8K is much bigger than on a NEVE or an SSL 9000, because it works under much less stress and much much less heat. So even if it wasn't recapped on the last 10 years, you should probably be fine, only fixing some problems here and there. I would advise to fully recap the center section no matter what. Then you can do it like our friend Marc Mozart did, and slowly recap each channel, while you use the console.
What's is the metering? Is it plasma or VU? If it is plasma have special attention if they are working correctly, these are not easy to find these days and sure not cheap!
Then I would suggest what Paavo recommended. Just make a full inspection/listening of the channels and annotate everything:
- sections not working (EQ, routing, compressor, sends)
- blown lamps/leds
- scratchy/faulty buttons (specially the routing matrix ones)
- scratchy/faulty pots
This will add to the final bill, since they are not cheap to replace.
EDIT: I don't know if this is you case, but just be careful with "buy as it is" deals, without having an opportunity to fully test it. These deals can quickly turn into nightmares.
Good luck!! If you decide do go for it I'm sure you'll have lots of fun and enjoy it a lot! These are consoles that with tender and care were made to last a life time.

Welcome to the forum!
Cheers,
Artur