I don't know that Pi3 would fail - but I suspect it would. Transcoding is CPU-intensive, and the 3 is about 150% as fast as a 2 - but I would even try it on a 2, so you'll have to draw your own conclusions. It would probably work for SD MPEG-2, might work for H.264, and would probably fail for HD H.264 (guessing) - and would certainly fail if you're playing with multiple streams.
You probably want to look into SAT>IP somewhere in there. That might be what you mean by "streaming server", but that would give you a local tvh setup in DE for recording, channel management, etc. that then uses IP to the remote one back in PL, which in turn has the tuners. Not 100% necessary, as Kodi could talk directly to the remote tvh backend, but it feels like it might be more useful. Indeed, I seem to recall that you can get SAT>IP LNBs, which would catch the signal in PL and send it all the way over a suitable IP tunnel to wherever you are...
