Re: bunk positioning
I have both of my smaller Starcraft boats on bunk trailers, the rollers are there to support and take some of the weight. I set my bunks about 28" apart on my 14' Seafarer and about 24" apart on my 14' Sea Scamp.
The rollers don't really have to be there, their more to protect the bow when the trailer is on an angle. I'd never run a V hull without at least having the first roller or having the bunks extended far enough and close enough where the keel couldn't hit the crossmembers. Most aluminum boats are super light, so bunk placement has as much to do with the trailer as with the boat. Keep in mind that many of these smaller boats were also meant to be car topped so their built pretty rugged. Make sure the bunks extend past the transom, especially if trailering with a motor mounted.
A keel guard and rollers shouldn't be a problem unless it extends down to the first roller when in place on the trailer. I've never even considered a keel guard on an aluminum boat but I guess it won't hurt. It will make it less prone to beaching damage. Most 14' aluminum boat weigh under 300lbs, if not under 200 lbs. I don't see any issues with the keel guard either way. If your concerned just lose the last roller.
