HTTR already available as a a pack to put into BFTB, Alti - to buy, I mean. Somewhere on the Matrix site. Get it if you can. The battles there are great, though there's only about 8 or 10 scenarios, much less than the original HTTR. The COTA pack is just about done, I believe and will probably be sold within a couple of months or so. That is to include all the COTA scenarios, I think, so will be well worth it. There are great, interesting battles in COTA. I still play on the old COTA, which has less options than the BFTB engine, less info available, and I assume isn't so sophistique - but - to be honest - I haven't really noticed (it works fine, anyway). But not worth buying original COTA now when you can get the pack in a couple of months.
You should try Manhay Crossroads next, from BFTB. As Axis. That is tough, but small and manageable, again, like Hofen (about the same size as Hofen). The RL battle was a real turning point, I think, in that Manhay was where the Axis advance ended up getting funnelled when it couldn't get anywhere in the north. It's a very challenging scenario. I've never won it, I don't think. You start off strong (as Axis) but the allies get a lot of arty to cripple you with. I have no idea how to win it.