Freezing improves the yield of juice. On a weight basis and with a press I expect 82 to 84% juice yield. I wouldn’t bother coring, running a traditional grinder doesn’t core.
With my Mom’s bag I would expect 40 to 50% yield. ,,, I freeze. I also get anxious and lower yield by trying to do it all in three days. Longer is better, a week is good enough. Thawing is important too.ie if you can afford a press next month freeze till next month.
Jolicour in the new cider maker, has drawings of a simple press for ciders which is sturdy plywood with bolts on the four corners. ,,, I lived over a decade before inheriting a traditional acme screw press in the wine club.
Pears have a delicate flavor. Oxidation can cover this. I like tannin as an antioxidant and either use crab apple or the bottle of tannin. US pears don’t have tannin. SO2 is important. Basically any cider recipe could be followed.
Gallons? How many kg or lb? Juice proper with low pressure press about 50%.