Longrod-- Unless I'm mistaken, you're building a Bateau.com OD 16, right?
In such a light boat, I don't think you'd be happy with the Merc Bigfoot, which is designed for pontoon boats and heavily loaded craft. I expect you would be disappointed in the top end speed, and probably speed through the range as well.
If the Johnson is an older motor, pre-Bombardier days, I would be careful as the OMC bankruptcy was a result, in part, or quality issues with their engines. I think Bombardier is now making replacement parts on a limited basis, but if something goes wrong, then you might be stuck with a motor that can't be repaired. If it's a new motor, then it should be a good one, except for the tilt business. Trim-and-tilt is great for fine-tuning motor performance and running in shallow stuff, but if the motor has a shallow-water drive option, and you do most of your running in deep water, a non-trim and tilt engine might be a good choice.
I have a lot of respect for Tohatsu motors after running one for six months. A lot of work boats in this area are now running Tohatsu OBs, for whatever that's worth (it might just mean that they're inexpensive). For service concerns, you have the added benefit of getting service from Nissan OB dealers since the motors are basically identical.
I've run Yamahas and I like that brand, but they cost more. I've run Suzukis, and I like those motors as well. Honda has a pretty good reputation, but there were a few years in the early '90s when I heard quality complaints against some of their kicker motors.