Can't speak to 1 (don't have a TC device).
For 2...not really, depending on how open you like your airflow. About the only add-ons I'd consider seriously would be a DT adapter (if you don't like the included one or like to play around with your own) and maybe a SS tank if you'd prefer a 22/23mm tank (if you want 22 mm IBTanked and Spectrum Tanks both make excellent replacement glass tanks - they hold around 6 ml, but are around 22 mm OD). Nano kit is also an option if that's something that appeals to you. None of this stuff is really necessary, though. If you're not in the EU, and ordering direct from I2R, consider picking up any accessories that look interesting, since they can be a pain to find in stock at US resellers, so you can save some pennies on shipping.
3) Absolutely - my go-to mix is 50/50, and I've never had a leak. I used to sometimes get a little bit of flooding on the initial fill, so now i close off the AFC, fill, blow a quick puff through the DT before sealing the topcap, then seal and open the AFC. I'd sometimes get a bit of gurgling on my first few hits before I started doing this, especially if I took my time filling, but have had no issues at all since I started. Never had any flooding/gurgling issues when topping up/re-filling the tank, and any first-fill gurgles usually cleared within a couple of draws even before I started preemptively de-flooding.