I also would second Aggie's suggestion if you can. I have a single tank, two double tanks, and a tank that takes four reels of 35mm. I don't think I'd go much bigger than that, I think agitation gets tricky with those eight reel tanks. Having said that, I find I rarely use the single tank. Somehow I can always burn through more film! If you are using more than one tank, start your development times at one minute intervals. Of course, I acquired these tanks slowly over the years, and still would like one more four reel tank!
-Suzanne