Mix and match stuff is OK, it works, but why not just buy a full 105 groupset, as mentioned above? I don't see the point of getting a Dura-Ace BB, FD and Ultegra RD and then using Sora shifters. The OP mentions that he'd like 105 shifters, but they're too expensive, but will upgrade to them as and when.
I'm sure Dura-Ace + Ultegra + Sora will work well, but that's like wearing an Armani suit and Valentino shirt, but wearing Primark shoes! Seems to be a bit of a daft idea.
I don't trust those Carbon components from Ali-Express, either, nor the Ti skewers. As mentioned, best to just sell the T3 and buy a new bike.
For the cost of £370 (£570 with power meter) on the OP's listed components, may as well just upgrade the wheels and tyres on the T3 and put the money towards a better specced bike with full 105 or Ultegra groupset.