For your shoes, I would probably go with a tri-specific road shoe for 3-bolt assuming that's what your Specialized Transition is for. They're faster to get on/off than a true road shoe, and you can't train enough to gain back the seconds lost in transition with an inferior shoe situation.
Next, 3-bolt, sure. But, if doing triathlon stuff or TT with that one bike..........Speedplay Zero with the aero cleat cover is the way to go.
In that case, for you, I'd buy one pair of shoes meeting the following guidelines:
-tri specific shoe closure (faster transitions)
-4-bolt Speedplay specific shoe, to get lower stack height and aero benefit of the Speedplay aero setup
If this is purely recreational on both bikes........get a really nice pair of 3-bolt road shoes. No need to fuss with the tri/TT style cleats and shoes.
Now, some folks have had success with maximum triathlon aero with Speedplays by going with laceup shoes. This is slower in transition, but, you swap in your elastic "lock laces" like you'd run in your running shoes. You're not sprinting in a triathlon or TT, so no need for the vertical up plane of motion to be as fixed.
Probably the fastest shoe you can run in a tri is a Giro SLX that you've swapped lock laces into and run Speedplay Zero Aero setup with. People haven't tested the newest rear-boa from Bontrager yet that I know of. That'd be a good option too since the boa is out back instead of on the sides.