I use the Live Another Life mod to start out owning Proudspire, and RP as lesser nobility.
Skills
One Hand, focused on swords
Block
Speech
Heavy armor.
Starting out following the CW for the imperials.
I suggest you use enchanting(not smithing) and some healing, based on the Morrowind description of the knights. Otherwise I think it looks good skill-wise.
Of noble birth, or distinguished in battle or tourney, knights are civilized warriors, schooled in letters and courtesy, governed by the codes of chivalry. In addition to the arts of war, knights study the lore of healing and enchantment.
Harder to make a comment on the RP. "Knights" really doesn't seem to be something that exists in mass in Skyrim. The Nords are more likely to be warriors. Small distinction, given the similar trade, but still there. Knightly orders are few and far between it seems. Of course, as Kodlak says, "The difference between a noble band of warriors and a ragged bunch of assassins is as thin as a blade's edge". Bands of "noble warriors" and knights wouldn't be too easy to distinguish, if you only look at their roles, in Skyrim, I think.
I wouldn't even use any profession - but that's just me. I feel like a Knight doesn't do anything petty like work. If I had to pick a profession - I would agree with Droid that Enchanting makes more sense as it seems a more noble magical and intelligent cause than getting your hands dirty. (yes this sounds facetious, it's rp).
I can't play without a horse.
I too use the LAL mod. One of the best additions for the game,by far. An absolute must have for every playthrough.
Another, for the horses, is http://skyrim.nexusmods.com/mods/14950/?. I can't play without it either. Just getting used to the gathering of plants while on horseback is a spoiled pleasure that holds an addiction without cure.
As far as you focused skills, they are almost identical to the suggested skill set discussed in http://www.gamesas.com/topic/1477061-orc-sellsword-archetype/page-2.
The OP's calculator link should omit the HA perks and complete the Speech and Block trees.
That is an interesting concept. However, there aren't any that come to mind right of hand. One could ask in the Mod Forum or browse the Nexus.
However, AFAIK... only the PC can initiate combat form horseback. I don't think the NPC packages allow for that. I believe it's hardcoded and thus unable to implement it.
Picking [censored] off as an archer on horseback is insanely hard and fun to do
Meh I've only tried it once and getting your aim correct and kiting enemies that run just as fast as your horse kind of makes it difficult to turn it around to get the side saddle shot.
I see what you did there.
Quite true Mic. In fact it's damn near cheating. I mean horseback combat in general, but especially archery. And a glitched feature that opens the inventory of a fallen foe automatically.
Bears, spiders and any other enemy is toast when caught in a circle run of death.