I fully understand your desire for a new motor. I bought 14' Lund aluminum boat that had a 30HP Johnson on it. The Johnson is manual start, won't start reliably, and my shoulders tell me that I'm not going to like tugging on that starter numerous times in a day of fishing. So, I recently bought a new Merc 20HP Four Stroke for my 14' Lund. Here's what I found with regard to buying online, pricing, availability, etc.
Tohatsu vs. Mercury: Yeah, they come off the same line. It's not real clear in the Mercury documentation, but if you go online and look at the details on Mercury's web site, you'll see they list manufacturing plants in Japan in partnership with TMC, which I'll assume is Tohatsu. It really comes down to features, and the Mercury had a better tiller arrangement than the Tohatsu for what I wanted. There are differences in the warranty, so you need to look into that.
Online versus offline: This is the first new outboard I've ever bought, and having a local dealer is of some value to me. I just was less than comfortable buying a new motor online. If I was shopping again now, I might look a little harder online.
Price: I bought my Mercury from a local dealer for about $60 more than the online price for the 20HP Tohatsu and $190 less than the online price for the same Mercury. To me, that price difference between the Merc and the Tohatsu is minor. I have my preferred tiller arrangement and I have a local dealer to go back to if there's an issue. The nearest Tohatsu dealer to me is a several hour drive.
Availability: When I was looking, the online site had outboards available in the size I wanted. Today, they show as out of stock. I ordered my Mercury from the dealer with an estimated delivery date of 14 weeks later. The motor was delivered to me in 8 weeks. Dealer told me they don't have a real good way of telling exactly how long it will take.
Bottom line: The new motor is hung on the boat and I'm ready tog et out on the water to break it in as soon as my schedule and the weather line up.