Much of what you ask depends on your budget. If you can afford it, by all means get a tribike. The advantage of this is you can have your present road geometry bike to train on in the early and late season and use for group rides( if you do that sort of thing). If you are thinking retro-fitting your road bike with aerobars and a forward position seatpost be aware that you could change the handling properties of the bike and it may not handle as well. I did this and it worked out ok but I also bought a tribike the next year.

Additionally, if you want a very aggressively low position it may not be possible to achieve this on your road bike because of a higher head tube than on a tri bike.

You also need to ask yourself if you are more comfortable riding in a road type position or want to ride in an aero position. If the answer is you want to ride in a "big slam" type road position then get some shorty aerobars and keep the bike you have.

Also If you get the aerowheels for your road bike now and decide to get a 650 wheeled tribike later you will end up needing another set of aero wheels.

Richard