There is no need in
Canon TC-80N3 anymore. You can buy a replacement on ebay which does exactly the same while it's three times cheaper than Canon TC-80N3 remote control($65 including postage). Also there will be no need in modifying its connector as it's sold with a right connector for each particular model. If the link above won't work just search au ebay for "timer remote 400D". The guy who sells them also has a Battery grip for 400D with built in timer and LCD display for sale but I guess it's better to have just a wired timer remote control as you don't want your camera to shake everytime you start the shooting session.
Re T-Ring: if you are going to use Stilleto focuser don't buy T-Ring for Canon EOS from Bintel. It suits fine Canon bayonet fine but unfortunately it doesn't suit Stilleto at all. If you are not going to use it any T-Ring that's suitable for Canon EOS will work.
I can't give you advice on T-adapter but there should be plenty of them on the market. They can have an extension tube which adds more space and can even accept eyepieces. I was using something similiar before but because it's 1.25" and it adds too much vagnetting to the edges I've decided to move to 2" T-Adapter.
cheers,
Michael