The Ultimate Pseudo-Historical Fantasy Campaign

I'm planning on running a pseudo-historical fantasy campaign in the near future. I'm gonna set it in some far corner of Siberia, but from the player's perspective it will start as a traditional fantasy game using Swords & Wizardry (or LotFP) for character creation. They wont necessarily know they are on earth, at least not at first. 

I want to use certain old school tools, such as using the advice of starting small in a 100 x 60 mile region using Underworld & Wilderness Adventures to flesh out castles and rulers as we encounter them. if they leave the starting region we'll use the Outdoor Survival map and random encounters from U&WA. 

Dwarves and Halflings are allowed though they are rare and common people will be leery of  them. Elves are evil, I'm gonna use the Elves from Lion & Dragon and run them like Melniboneans, cruel and haughty Fae, stealing children, and luring men under Elf Hills and such.

Depending what the players do, and how long this runs, I have some ideas of what lies to the north and the south. If they go north they'll pass through Blackmoor, LotFP's Weird New World before reaching Mount Meru at the North Pole, where they could discover the openings to the Inner Earth. For that, if it ever happens, I'll use Grimm Aramil's Lexicon Geographicum Arcanum Vol. 1: Species of the Hollow Earth. If the go south they will discover China and the Silk Road (Sword & Caravan). 

I also plan on using a custom version of Jeff Reints' Random Campaign Advancement from Flame Princess Zine #6? Which will slowly move the campaign from high-magic fantasy to mundane low-magic historical. So, dwarves could fade away, or magic and magic-users, or even clerics could lose their abilities. It will all be random so, in classic old school fashion, I have no idea how this world will play out. 

I want to throw in the Lost Dungeons of Tonnisborg somewhere in there.  

I imagine this will be the ultimate campaign that plays out over several IRL years, but who knows, you know how these things go. Plan big, prep small. or something.