As with the 3rd person view... well, again, it doesn't matter what you use just so long as you use it and do it well. Making your own engine is a very big endeavor to handle. For what you've described about your project, making a new engine would be reinventing the wheel. Everything you've described can be done in the two engines. For now, I wouldn't meddle with the overhead of making a custom engine. Instead, I'd start implementing the basic elements of your game into an existing one and see how things go from there. You may find that your OOP models don't work as well as you had thought- perhaps you'll chance your mind on things you wanted to add.
Go look at the feature list of the two engines. Remember that the features aren't final. If they don't do some of the things you want, then add them. Both engines are open source.
I know about reinventing the wheel... I would rather use a rendering engine that I don't have to build from scratch. I want to start experimenting.
Have I ever written a game before? Gee, I really don't know how to answer that question. I have written some Tabletop RPGs using minitures using several different genres.
Using Dromed under the Thief2 engine, I've built about 13 missions. I've had to write schemas for the voice index and did most of the recordings as well. I've gotten some friends to generate some new models for me which I implemented into the game's object hierarchy. Not to mention those 7 AVIs... Since I've started my research, I haven't worked on it much, and I'm going to miss my Oct 31 release date for the next pack of missions (1-10). The T2 stuff is only a hobby since I can't make a dime off it. All my custom AIs and voices are mine, which I can leech from it.
I'll look into it more...