Attempting DIY Long tail motor build. Help?!?

Okay so about the boat. I recently purchased an Aluminum flat bottom boat for a really good deal. That being said, it needs a little (I hope) tlc and a lot of help from you guys! It measures 18’ in length, 32” width at the bottom and 48” width at the top. It is riveted and is a MonArk built out of Monticello Arkansas.
For starters, it has 3 pretty good holes in the bottom which I’m confident I should be able to fix (confidence doesn’t always bond to aluminum). The holes are from nickel to half dollar size I’d say. I’ll attempt to attach some pictures of what I have done thus far. The method of attack I went with was to cut some “patches“ out of a piece of sheet aluminum and then use the famous AlumniWeld brazing rods from the local harbor freight to attach said patches to the exterior of the hull. After completion of all my “welding” on the patches, I’ve yet to decide on the next move.
Would painting over the top of this be sufficient in helping seal everything tight?
Or is there some sort of spray/ paint on sealant that would help just generally seal everything? It is an older boat and it is riveted so I would fully suspect that at least one or two rivets or seams have tiny leaks.
Then there’s the motor. I’ll be mostly in the Arkansas River backwaters, Lake Dardanelle. I could forsee myself being off into some shallow bits of water but I’m honestly not really certain on how often I’d need a mud motor but between budget and being a duck hunter, I’ve decided I’d be willing to give up some mph for the versatility. My question now is size of the motor I’d want/ need. I’ve got my eyes on a Honda 190 or of course the predator 212. What’s the better option here and is either gonna be enough to move be around with a passenger it two and some fishing gear. Nothing crazy. Maybe a couple 30’s of some Busch Light.

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Personally if you weld them, there shouldn’t be any issues. You could do a coat of 3m 5200 over it if your worried.

Any longtail is going to be slow. Not sure if you’ve looked or not, but MudMotor Talk forum has a ton of threads and information on exactly what you’re asking.

For motor size I’d look at a minimum 16 hp which will be slow, and up to a 23 vanguard which will be slightly less slow. I had a 24hp honda longtail that I really liked as far as longtails go. That boat you have is a really nice size and shape for the LT.

Judging by the condition of the boat that you posted I’d also recommend making sure the transom is in good shape and reinforced properly or at least has good solid wood in it.

For that size boat I’d be looking to put a 9×6 or a 9×7 prop on it if you end up running a 23hp. Not sure if you decide to run a smaller motor.

Well, it’s not actually a weld. It’s just brazing it. Honestly not sure the difference but I’ve read several forums posts About them and those first two sentences or in just about every one of them LOL so I felt it necessary to say that much haha. I will say, the tensile strength is supposed to be greater than that of aluminum and on a flat piece of aluminum the “weld” is most certainly the strongest point

I hope I’m replying directly to you his, this is actually my first forum post ever so I’m totally new to it.
I really appreciate such an in-depth and informative answer! Super helpful that you’ve had previous experience with the same size boat. About how quick would that 24 get you moving? Honestly if I can get 7-10 mph with it loaded down on calm water I’d probably be pretty content! I’d need to be able to go upstream but it would be minimal current. I don’t really see myself ending up main channel. Not in that boat, at least not for now! Could someone weld that for me for a decent price somewhere here local?

That 24hp pushed my boat about 18-19 mph. What kills speed on a long tail is load. Everyplace you can save weight helps a long tail. A 16hp would push you over the speeds you are talking about.

Awesome, much appreciated. I’ll be looking into some added support for the transom that’s also weight saving