Didn't you just start a completely different thread about the same topic? I would have thought that one was sufficient.
It seems like the best way to make use of Combat Reflexes, Threatening Demeanour and Never Outnumbered is to use a reach weapon. Unfortunately, the only one-handed reach weapons are a kobold tail attachment (seriously, be a kobold) or the "flickmace" which appears new and somewhat controversial as it was apparently printed without flavour text which is suspected to have been important.
I would actually say that Bushi Warder is a pretty sensible entry since it gives you both your prereq feats and, better, you can use Int for Combat Reflexes. I previously pointed out the discrepancy with using Zweihander Sentinel but actually it does grant you Scarlet Throne if you need it and doesn't lose you much so I guess I can take that back - but only if you're expecting to go into Landsknecht at L6 and never come back.
Bushi actually works for pretty much any of the base classes. A Stalker with the Vigilante archetype would probably work pretty well too; that gives you Scarlet Throne and Primal Fury, or you could take the Lord of War Stalker Art at L1. Either way you get Quick Draw and EWP (Katana) means you get a one-handed weapon which does a tiny smidgen more damage than most (but still not as good as a greatsword).
Controversially, though, I'm going to suggest Vanguard Defender Warlord with a Spiked Bashing Shield and Iron Tortoise Stance. You don't get the same benefit from Threatening Demeanour but because you threaten 10ft, Never Outnumbered is going to work better. At L9 you get Superior Reach which ups this to 15ft! You're still using a one-handed weapon so all the normal stuff applies, but your base weapon damage is better and you get an AC bonus too. This is probably comparable to Scarlet Einhander, but reach is king so this is better.
It really depends on what options you're going for. All Landsknecht means is that you're probably fighting one-handed. You don't actually need Scarlet Throne or Mithral Current to get in (though probably you will want them to meet prereqs for later manoeuvres) or in fact to use them at all (though you probably want to). Personally I greatly dislike Mithral Current, because it's stupid. But with the exception of the ranged schools and Iron Tortoise (notwithstanding the above) and the possible exception of Thrashing Dragon which is quite two-weapon-focused, you can pretty much use any base class schools just fine. There's really no reason why you couldn't e.g. go Mystic, possibly get Scarlet Throne through a trait or something, and then focus on Riven Hourglass and Elemental Flux which are probably better manoeuvres anyway.
You could even consider e.g. a Swashbuckler entry. With the Practised Initiator trait you get +2 to IL, so a Swash 4/Warlord 1 (or Inspired Blade Swash 4/Warlord or Vigilante Stalker 1) could enter Landsknecht and still have full initiator level and the highest-level manoeuvres available. There's probably a lot of synergy there and it opens up Dex-based with Slashing/Fencing Grace or Deadly Agility if you so wanted (though it's not clear how, if at all, that works with Strength of Arms).
In short: probably needs a bit more direction, since there are many options here ranging from straightforward to a bit wacky.