[Liam]

You want the thin resin for layup,you could use the thick for making thickened resin for filler but I would just and more cabosil to the thinner resin rather than ordering 2 different resins,yes you can fill those voids in the deck edge with the peanut butter,for larger holes think about adding some 1/4 chopped glass.

As you are seeing the orginal glass work was pretty shoddy,you should be able to do a way better job. I had the same glasswork peeling off in the bilge,but mine was not the original work,someone had redone mine in the past,i was able to just peel it all off. Get as much off as possible,gind and fill all the edges and spread in some slightly thickened resin. Once you have tabbed in the stringers I would lay a fresh layer of 1708 or CSM in the bilge for extra protection.

I have not installed my deck yet I am buried with yard work right now but there are 2 schools of thought on wether to overlap or not. Obviosly it will make a stronger more watertight joint but it will also create a raised area which will need more fairing.
You need to put a layer of CSM after the 1708 on the topside of the deck,this will stop the weave showing though and cut down on fairing.
You want to grind down your perimeter enough to allow for some 1708 to overlap and then the top layer of csm to overlap further without you work ending up raised compared to the original glass.

Also you will find 1708 does not work well on corners,it does not bend well,i found it best to chamfer the top of my stringers and limber holes to allow the 1708 to work better. Make a fillet of thickened resin on any insde corners that you are going to cover with 1708 as you will not get the 1708 into 90 degree corners either. Make the fillets when you are ready to lay the glass,that will make a stronger joint(wet on wet).
While you are in the bilge area,providing you transom is good you may want to cut a mousehole and fill with resin and 1/4 chopped strand around the garboard plug,then redrill for a new garboard plug,leave the outer layer of the transom glass in place and fill from the inside,this will increase the life of you transom.