If the primary "failure" that you had with the 4-gallon make was a problem with getting cheddar to knit ... and that was your first cheddar ... that may not reflect a problem in your techniques. Cheddar is inherently challenging to get a good knit, due to the cheddaring/milling/salting that it undergoes. By the time you get through all of that, the curds are tired and just want to be left alone, not forced to bond with their neighbors.
How much pressure are you able to apply with your press? Cheddar will require higher pressures -- and this is a place where make size can make a difference, simply because the larger mold used to hold a larger make has larger surface area. For example, 100 lbs applied to a 4.5" diameter mold may be more than enough to close the rind, but 100 lbs applied to a 7" diameter mold may be not nearly enough. In the former case, you are getting 6.29 psi, but the in latter, only 2.60 psi (assuming I have done my math correctly).
Bottom line is, if you want to make cheddars (other than something like a Lancashire or Caerphilly) in larger quantities, you will need a press that is capable of giving you the pressure that you need. Keeping the curds warm will help, some, but you'll still need plenty of psi. Note that a make that is not milled -- such as a gouda or a parma -- could be pressed initially while under whey, which will help even more with the knit. But with cheddar, that is not really an option, since you have already salted and milled the curds.