Batts for tinny

Can't answer all your questions, but an AGM is the go. I have used one for a while to run the elec motor on our canoe. Benefit is you won't spill acid when moving and carrying. If you need to, you can carry and use it on it's side. This is how I use in the canoe, shoved part way under the rear seat. And it holds it's charge well. If not used for several weeks, it will sill be charged when you need it.

An AGM battery is theway to go. Suggest you get a plastic battery box (most marine dealers them) and battery terminals with wing nut connectors. Need to work out a way to sucure the battery box when boating (bit of a pain in a open tinnie). Battery in box is the easy and safest way to carry in car when not boating.
Also your 10hp only needs a small battery 35/40 ampere hour, if you have the rectifier charging kit fitted to your motor.
The engine you have is the easiest pull starting 10hp on the market. If you are physically capable I would just use as a pull start. Save heaps of drama when travelling.
If you need the battery for nav lights you can get around this, there are tourch type red/green navlights and white rear ones for not much money available.

Stay dry.