Welcome to the site.
I don't know about the JB weld repair on the fuel tank. I am not saying it won't work, I did some JB Weld on a weed eater once and was succesful, I am not sure I could trust that repair on my boat. Getting towed off the water is a PITA and takes the pleasure out of boating. I also don't play with fuel leaks due to the explosive manner in which fuel leaks are typically found.
The 120 hp outboard is a very tough and capable engine. Rings are fresh in yours so make sure the lower unit is serviced and you have a fresh water pump. When changing the gear lube in the lower look for signs of water as lowers are not cheap to repair or replace.
The most important guage IMO is the tachometer. Then water pressure and or temp guage(s) and voltmeter.
When you get the tach sorted out you can test the prop to make sure the boat is propped right. What you will be looking for is a good hole shot and that you will be within the manufacturers recommended RPM at WOT. It may be propped too high which would give you that feel of all or nothing. The throttle and shift cables are normally adjusted correctly if it idles and shifts properly. That is my .02. Congrats
