Soft plastics/ soft plastic vibes would suit the low retrieve rate of the Alvey. You might find line twist a problem. It will build up with all the casting and retrieving.
If possible it's best to avoid angle grinder for cutting. They run extremely fast and the disks are prone to jamming and shattering. There is something about aluminium which tends to make disks jam.
You could just sand it first. If you are still keen on an acid wash then something milder like vinegar might be better. If only for you health - hydrochloric acid produces fumes that are very hazardous and you will be working in a confined space.
I would then use an etch primer, followed by primer and a paint with good water resistance.
Acid will eat away the aluminium. It's not a good idea to leave the hull wet for long periods - as you will get that sort of corrosion. There is a name for it (I don't recall at the moment), It could cause significant damage eventually.
A wire brush or wheel should be stainless steel and not carbon steel for cleaning aluminium. Also it must be clean and not used on any other type of metal.
Fortunately fiberglass is amenable to repairs. Where it goes all the way through the hull you will have to cut up the floor and glass it from the inside. It's not that difficult if you do your homework and are reasonably handy.
It makes more sense to bring it up to scratch than changing the whole structure with a centre console conversion.
Have you thought about getting an inflatable? Much more stable and seaworthy, more amenable to being powered, no need for roof racks so easier to handle on your own. Some of them are considerably cheaper too.
"BUT REALLY, THIS IS AUSTRALIA and one of the least populated places on earth".
They are doing their best trying to change that. We will have 60 million around the end of the century under current policies.
A penetrant fluid would be better than WD40 (though WD40 make one). Apply it over a few days. You have to be very careful you don't damage the nut. Make sure the screwdriver is of the optimal size.
Yes it's gets more complicated the more I think about it as the breaking strain of the braid is an unknown factor. Often it's a lot higher than the rating, so you can't be sure if the leader or the braid is stronger unless there is a big difference in stated strength. But at the end of the day if the joining knot doesn't break in a direct pull then it's doing well.
It depends how you express it. It's a 100% (at least) compared to the weakest point - as evident by it breaking elsewhere. So for practical purposes you don't need better than that.
FG and other knots tied in single braid seem to work with heavy leaders, for light leaders I always tie a bimini double.
I tie a bimini double in the braid (at least 40 turns) and then use a double uni to the leader. It seems to be 100% as it rarely breaks at the join when busting off from snags.
Another point is to have the vent line going at least slightly up all the way (apart from the water trap). If you have any low points they can fill with fuel and the tank won't breath properly.
I would vent it outside of the boat, no point risking any vapour build up and explosion. Also the vents should be angled so the open part is pointed towards the stern to minimise water pickup.
Condensation is a myth according to some (and I tend to believe it). You can get water through the breathers if you don't have a trap in the line. It's possible to pick it up from the service station too. A poorly fitting filler cap is another potential source.