First thing, if you are reloading, is to get/buy/borrow a current reloading manual, preferably published by the manufacturer of the bullets you are using.
There is a lot of data out there. I have several CURRENT reloading manuals. Be careful of any of the manuals that are over 10 years old, as those loads tend to be pretty hot.
Wolfe publishing has a web site
www.loaddata.com which is very good. You have to pay an annual fee to use this service. They also publish the Rifle and the Handloader magazine.
Second, realize that a lever rifle does NOT have the strength of a Ruger #1.
Third, get a sissy pad or a limbsaver recoil pad, because you will need it with a lever rifle.
The drop at heel of lever rifles can make you very aware of recoil.
I would suggest 300-350 grain bullets as a starting point, and then you can go up to 400 grain bullets.
I have used all of the weight bullets, and of course as the weight goes up, so does the recoil.
The 45 caliber can be a lot of fun, and can be very accurate.