Welcome to GBO! All bases for the Handi are aluminum
except the Warne bases. Green or purple loctite should be used, blue can too, but it requires heat to remove the screws, finger nail polish will work too.
Lots of folks like the Rifleman rings, they're an economical ring that are sold at Walmart, very popular.
Aluminum or steel, your choice, both work.
Depends on the scope, I'd say you can get by with mediums on the Leupy, the small power ring and tapered ocular bell helps, doesn't matter about the objective size, plenty of barrel clearance..
Be sure to spend some time in the FAQs and Help sticky, there's an answer in there for 99% of your questions because someone before you has asked.
Tim