Grains per cartridge and paper over primer
You are right, depending on the bullet you use, you may be able to fit 30-32 grains in the case. I fit 30gr in with a 200 gr RNFP bullet, over powder card (fairly thick one) and a grease cookie that was about 1/8 inch thick. So, there's lots of room for more powder if you delete the grease cookie and use a thinner over powder card.
I loaded about 20 452190's today, with a thick over powder card and no grease cookie. I seated the bullets so that the crimp was just about where the bullet starts to neck down towards the nose (probably 3/16th's above the top grease groove). With about 1 or 2 /16th's compression I was able to get 28gr by weight of 3f in the case. I could probably seat the bullet higher and get more, but this is my starting load for this bullet and will work it up an down till I find something the gun likes.
As for the paper over the primer, this is sometimes used in Long Range BP Cartridge Rifles - discussed by Paul Matthews in several of his books. The notion being that the old primers did not deliver as much heat/flame as the new primers, while also delivering more hot debris. Black powder apparently likes the hot/flaming debris more than hot gas. Modern primers are a product of smokeless powder which likes lots of hot gas. The idea being that if you put a piece of wax paper over the bottom of the cartridge, you dissipate those gasses quicker and provide a bit more combustible material to ignite the powder from the base of the powder column. This might provide a more even burn than would hot gasses going nearly all the way to the base of the bullet from modern primers. There are several Long Range BPCR guys that now use small pistol primers held in by a shim-ring on their rifle cartridges, creating less of a primer charge. I haven't tried that yet with my 45-70, but may do some day...
I'll let you know how I get on with the rest of my load build.