Regarding flat face quick connectors, you could just as easily use them with rear remotes. Doesn't make a difference where the hydraulic fluid is coming from.
Regarding grapple weight. I agree that mid three hundreds is no biggie. However, mid 400 range is really starting to cut into your net lift unless you have a 2000+ lift capacity. Using your own tractor as an example, with about 1600lbs lift capacity you will have a net lift of 1150 after mounting a 450lb grapple. I like to think that a tractor can lift a full grapple of almost anything other than granite but remember the load is not at the pivot pins so capacity is less, maybe 75%, of calculated. That means maybe 850lbs real lift capacity remaining. Three 12" by 8ft logs would weigh about 900lbs. That would be close to capacity (probably could lift a bit more as you wouldn't lift to full height). So for your tractor a 450lb grapple would be stretching it but probably OK. For any lesser loader capacity though a 450lb grapple (not that uncommon) would be silly as the loader couldn't manage any "heavy duty" load because of the grapple weight.
Dealers and manufacturers are really not very sophisticated about CUTs and grapples. They both tend to oversell and advise buying larger and heavier grapples than really make sense for CUTs. Virtually no CUT under 55-60hp (which is probably the upper limit of CUT anyway) can overpower a light duty 300-350lb grapple. Why spend more money for a heavier grapple that will only limit the amount of work you can do?