Your main filler will be SMC (Silicified microcrystalline cellulose).
Your lubricant will be a mix of Stearic Acid and Magnesium Stearate 2:1 respectively.
Now you want to use 1% of the total weight of the final tablet or mix
Say you want to prepare 1kg of powder to be pressed
you want your tablet to weight 250mg and want 25mg of active Ingredient.
250g of active ingredient
740g of SMC
10g of lubricating Mix (2:1)
Now when you press your tablet will contain 1% lubricant mix (ie: 2.5mg per 250mg tablet)
as for mixing the powder, I suggest a GMP compliant V-mixer. Essentially a V-Mixer is a
hallow V with an opening somewhere. this V is attached to a shaft which rotates
on a horizontal axis. So it splits the powder in half then recombines it over and over.
This gives you a uniform powder.
The V mixers usually have NO DEAD spots where powder can accumulate and not get mixed which can have serious consequences. A good size mixer can cost 1500$ or you can simply buy the V and attach it to a motor. Really up too you, but its critical that your powder is well mixed; not only would you end up with unequal dosing but your pill might not press well due to too high or low concentration of lubricant.
I hope this all helps. Let me know if something is unclear.