The largest stretch I have done was 38 x 96, and I would not really want to do that again. Most stretcher bar comes in max 9 foot length, so going past 96" is hard to do. I do 36 x 72 on a pretty regular basis.
I use a dinning room table, with a piece of 4 x 8 blue foam (housing insulation) in the 1 inch thickness. On top of that I use cardboard of regular thickness. Then I cover everything with waxed brown paper. The waxed coating makes sure that the coated canvas will not stick to anything. But with Timeless that really is not that big an issue, as it is pretty hard to scratch a good coating.
My bar is the Larson brand, part 6011, all that I use. This bar comes with internal bracing strips sold under a different part number. This bar has a 1 1/2 height and again that all I use now.
Pliers are still the Breathing color stretch relief, still love them and use them daily. IMO the best solution I have found (besides a machine which I can't justify)
Canvas, is either Lyve or Crystalline both coated with Timeless (sprayed on not rolled).
I also have a pretty humid environment, but so far no real issues with slackness over time, you can get a drum tight stretch with the pliers I use. And so far, the Breathing color canvas has not pulled, or torn during stretching.
To Dan's point on gator for the larger stuff, I agree the workflow is a bit easier, but you still have to coat (at least I do) as during the glue down it's just too easy to get water or glue on the face and thus pull off the ink. Breathing Color canvas (for that matter any inkjet canvas I have used) is not very forgiving to any moisture on the face and the ink lifts off very easily. If you are going much past 30 x 40, I would consider 1/2" gator over 3/8" as the former is much less prone to warping and is much sturdier when being framed.
Paul C