Need information for adding tmcc to a semi-scale GG-!

Both the RMT and the K-Line are DC motors, so you can use the ERR Cruise Commander for them.  The only real sound choice is the GG1/EP5 RailSounds Commander.  The will double-head fine after the upgrade.  Electrocouplers are entirely up to you, you can omit them, have them only on the rear, on the front, or on both ends.

As for whether you can do the upgrade, that's clearly outside my control.  Only you can answer that question, I have no idea of your abilities.  My gut feel is I'd consider starting with something a bit less involved, though these upgrades aren't all that difficult.  Mistakes can be expensive.

I looked into it once because I had a couple conventional K line GG1s but decided it made more sense to buy a couple of the "same" engines with factory TMCC. Selling the conventional ones and buying the TMCC ones was less expensive. Adding the Cruise might change that.

As an aside, I did have issues with cast metal crumbling on the side frames on one TMCC one and found Lionel replacements worked well with a tiny bit of modification to a bump on the replacement frames that had to be removed.

I converted a 2360 GG1 to TMCC about 15 years ago. This is a twin AC motor engine. I kept the original horn for sound and this engine originally came with electrocouplers. It doesn't really need a sound board because those two AC motors make enough noise that almost sounds prototypical. 

I installed a Cruise Commander in my Williams traditional size GG1 along with ERR older Railsounds. It all fit. The new Railsounds board is much smaller and should make the job even easier. You can use the pantographs as the antenna as they as insulated from the body. They are very effective for this.

The engine pulls like a tank. I never tested how many cars it could pull but it easily handles my 8 Williams 18" cars.

Pete

Here is a conversion into the scale K-Line.  This engine is an extremely smooth running engine.  This was a Legacy conversion I did with various legacy parts and Rail Sounds for GG-1.  First series of pictures shows what came out (Reverse Unit and True Blast; and where I put Mother board/R4LC and Motor Drive board.  Last pictures have RailSounds installed.  Installing Electro couplers was also easy, but I had to use the non standard version that Lionel has for certain applications.   Mounting head is different to get right coupler height when installed.  G

Here's one I did a number of years ago, this was a really ancient Williams GG-1.  The biggest issue was the oddball couplers, they were permanently bonded to the pilots.  To get electrocouplers installed, I had to modify a pair of DASH-9 couplers and emulate the old Williams ones.

Note this is before I dressed all the wiring, I didn't really put the shell on like this.   I did end up using all the available space.