US means Mode 2 as 98% of fliers here use that. No your esc does not need to brand match your Rx. I don't know of any that come with the Futaba polarity tab but if they did that trims off in seconds with a hobby knife.
if you are going to be flying with others and/or in a club then best to find out what the other guys are using. 99% sure they will be flying mode two. If you are on the same mode as the others then they will be able to help you with getting the plane in the air and showing you the ropes. You would be hard pressed to find anyone to help you if you were flying a different mode to what they were used to.
I'm not sure how left handers get along on mode two, maybe another lefty could chime in?
The ESC doesn't need to match the TX/RX. I haven't heard anything about those HK TXs. But I have been curious. Myself, I am going with the Turnigy 9x. Very adaptable, and can run open source software. Mode 2 is what I am used to(not planes yet), so that is what I will be going with.
ESC should work fine with that ( and near all) RX's, thats a okay TX to start with, a bub of mine has one and I like it Fine , get some cheap 5 or 9 gram servos and a outrunner and your fly'in,