Here's a link to a recent discussion on washing in cold vs hot.
The gist is that the vast majority of cloth users wash in hot but not everyone. Hot water washes better than cold, the science is there to prove that. The real question is wether it's necessary or not.
I'd say if you want to try washing in cold then go for it. The worst that can happen is that you'll end up with stinky diapers and have to start washing in hot. You're not going to 'ruin' anything by trying with cold so if it's something you're interested in I don't see why you couldn't give it a try. You could also try warm as a compromise or maybe using hot every 2nd or 3rd wash.
As for the detergent, I really recomend not using that much detergent. It's really just not necessary and could cause serious build-up issues (which lead to really nasty odors and perhaps rashes). I know it's counterintuitive, diapers are dirtier than clothing so logically you'd think they'd require more detergent, not less. The problem is that modern detergents have many ingredients made to actually stay in clothing. UV brighteners and anti-stain agents simply would not work if they didn't stay in fabrics even after rinsing. For clothing it doesn't usually matter, they're just not asked to perform the same way diapers are so we never notice the build-up. But with diapers, the combination of urine/feces and detergent build-up can create nasty problems.
Using the full amount once is certainly not a problem and perhaps you could even continue for weeks, months or even years with no problems. But your diapers will get clean even with half the recomended amount (many use even less than half) so why take the chance? Plus you'll be able to make your detergent last twice as long...
I remember from another post you mentioned using All F&C and that your dh thought this meant you wouldn't get build-up. Unfortunetly that's not necessarily true. All that 'Free & clear' really means is that's it's free of dyes and perfume. While that's usually preferable in terms of possibly avoiding skin irritations, it really doesn't mean anything in terms of the possibility of build-up. Free & Clear detergents can (and usually do) have just as many additives as regular detergents. In fact, not to discourage you too much, but All Free & Clear is often listed as a 'use with caution' detergent because it seems to cause a fair amount of people build-up problems. Now, that's not to say that you shouldn't use it, I always recomend someone just use whatever they already have. I'm just mentioning it so that you're aware that it's not a guarantee against build-up.
Pre-rinses are optional but fairly popular and could be helpful since you take out much of the 'nasties' before washing, so you're washing in cleaner water. Same for the extra rinses, technically optional but fairly popular to help better rinse detergent from the diapers. The need for these isn't something you'd likely notice the very first time you wash your diapers, you'll see as you go along if they're steps you'd like to add. Since they both use only cold water the only extra cost really is the electricity the machine is using, that's probably a couple pennies at most so not something really worth worrying about.