Believe it or not, I think that is how that model of Sea King trailer was set up from the manufacturer. Mine is almost exactly the same.
1. This trailer was set up with the winch mounted above the bow roller and no way to run the winch cable or strap under the bow eye; I believe that was fairly common on older trailers and I'm not sure why that would be a significant problem. It can be a concern when trailering, as with a sudden stop the boat can ride up the bow roller, but if you have this fairly light weight boat secured with transom straps and a safety chain on the bow eye I don't think that should be too much of an issue. If it worries you, you could also add a hold down strap to the bow eye that runs straight down to the trailer frame. The elevated position of the winch also makes it more difficult to winch the boat up onto the trailer, particularly on a steep bank. I shortened my winch post (cut it down with a cutting wheel) until I could at least get the winch strap level with the bow eye, which gives you better leverage when cranking it up on the trailer. I think the only way you would be able to change the position of the winch strap/cable with respect to the bow roller would be by replacing the winch post assembly entirely or make dramatic modifications to the bow eye support.
2. Yes, ideally your bunks should support the transom. I just moved my winch post forward until the transom of my boat was where it should be. You could also cut your replacement bunks slightly longer, but I found that I needed more tongue weight and shifting the boat forward was preferable
3. You do want to support some of the weight of the vessel with the keel rollers, but not so much that it doesn't rest on both bunks. Not sure what the ideal set up is, I just played around with the height on mine until it seemed right. I would guess that the rollers are in need of replacement. I wasn't able to find any rollers that fit the back rollers on my trailer and had to replace the entire assembly. This one from Attwood (
https://www.amazon.com/gp/product/B003EEV364/ref=oh_aui_search_detailpage was very close to the right hole spacing for the existing mounting holes; I just had to open them up slightly. The forward most roller was another thing. I could not find an assembly that matched or a replacement roller, so I ended up shaving down a replacement bow roller using a drill and sand paper until it was a small enough diameter to fit the existing assembly.
4. My bunks are also on edge and I'm not concerned about it; there are new trailers that come with bunks in the same configuration. In theory, a bunk with a wider bearing surface is nice as it spreads out the load more, but I would think that given the reduced strength of the bunk that the span between the supports wouldn't support much and you'd end up with something closer to point loads at the support locations. Ideally your bunks would be as parallel to the bottom of your boat as possible; you could rip them to the right angle, but looking at your picture it seems like the aft end of your boat has a pretty flat bottom. Either way, it shouldn't matter much with such a light boat.