Nice one Soggy, glad you have decided to take the plunge!!!
I bought the TAE Typhoon, with the view of upgrading it in the future if I fancied it. I think you can add the extras on
But to be honest, I had my Typhoon in the lake today, and the only thing extra I have put on is a Subtech Pitch controller for the Dive planes, and it works well. I can make it hover, ( as long as your ballast is spot on ) run at periscope depth, and run fully submerged. So not sure what else I expect of it to be honest.
The pitch controller is pretty responsive, as are the planes, obviousley as long as its moving. So I might just stick with what I have.
I use the Robbe F-18 computerised handset. I have added a few extra switches etc, and I find it great for the subs. Its practically infinately expandable. Just tell your other half once you buy it you wont have to buy another one !
The new 2 Ghz sets I use for remote planes, there great but I wouldnt touch one for a boat. I have had some bother with dampness and signal loss due to water. The last thing I would want to introduce on a sub!
Paul