I don't have time to respond properly right now, but I think your math is wrong with the moulds. Cheese has about the same density as water, so you just need to calculate the volume of the cheese in ml to determine the weight of the cheese in grams. a 90 mm (9 cm) mould has an area of 63.62 cm2. That means that each cm of height will weigh 63.62 grams. A total height of 13 cm would result in an 827g cheese *but* it would be taller than it is across. That would be OK for some cheeses, but not for others. Also, you need about twice the height in the mould to accommodate the drainage of whey. So that means that generally you can have about 6.5 cm high cheese weighing about 413g (You can probably up that a *bit* for a cheddared cheese, but probably not that much).
For a Caerphilly you *definitely* want at least a 1:1 height to width ratio if it is going to be a natural rind (with geotrichum on the outside). Well, it's really about the surface area to volume, but I'm still trying to figure out optimal ratios so I'm mostly talking out of the hole in my head ;-) But anyway, if it's not tall enough, you will get softening of the paste *all the way through* the cheese. The main problem with this is that you won't get that classic cheddar-like, acidic core that's important in a Caerphilly. I would try to find a mould that's at least 2 times and maybe 2.5 times the width high. Also, another quick piece of advice if you are doing cheddars is to find a low flow mould (less holes). I have a high flow one and the main problem is that it's hard to make a cheese without marks. This leaves it vulnerable to blue mould. You can work with it, but you'll probably wish you didn't have to. If you are not going natural rind, then the shape and size doesn't matter at all as far as I can tell ;-)