I saw this 18 HP on Craigslist for sale and I remembered someone on here loking one. Hope this helps. https://raleigh.craigslist.org/boa/1192875176.html
I have used a rec-pump simular to this for years now and I have no problems with fish dying. I would give the aerator a try first. If you have a problem with fish dying after that then add a fresh water pump
Here's a great place to find bimini tops and all kinds of stuff for your boat. They specialize in jon boats. Great people to deal with. Bought my boat from them. www.akmccallumco.com
Good luck with your build.
I deal with a place here in N.C. that has just about anything you could ever need for your Jon.
https://www.akmccallumco.com
I have seen several center consoles in thier store and in thier catalog. Page 38 in the catalog shows 3 different kinds.
They are also some of the most helpfull people...