Thunderbolt 3 or USB 3.1 over USB-C should do away with latency altogether. Speed of the connection has almost nothing to do with latency. Latency comes from the system involved. the drivers etc. All you might gain at a certain point is more channels streaming in and out.
Every LE type DAW software I have had isn't a good representation of the DAW it's named after. Most are old versions that have not been updated for a few years. There is also very little info out on the web to help and even less people who have used it. Enjoy the instruments and loops you get with an interface but don't invest much of your enthusiasm in an included lite DAW. If this has changed I'm glad but that was the way it was when I last bought one. I agree with this but in my case I got Sonar X1 LE with a Roland keyboard, which is almost the saddest version I've ever owned, but I registered it and almost immediately got an offer to upgrade to X3 Studio for $99. The free X1 LE was worth over $200 as a doorway to upgrades.
The same applies to my Cubase 5 LE I got with my Tascam, Right now I can use it as an upgrade pathway to Cubase 8.5 and I believe I would save over $100. Being a registered customer comes with perks even if the software is not top self. I use Cubase 5 LE all the time and it might be basic but it sure does a lot for free. Sonar X1 LE however is real buggy being X1 I guess. I installed it on my office computer just for the heck of it and to open when helping people who might ask questions about that version. It did not even include TTS-1 which would have made it some what useful.
I found little value in the Software that came with my Scarlett,, they were inferior to what I already had with stuff that came with Sonar. Tascam's will now ship with Cakewalk SONAR X3 LE and Ableton Live 9 Lite
The Tascam us2x2 has MIDI and also has the option of wall power, the 2i4 is only buss powered which causes issues with phantom powered mikes.