I have a pretty good accumulation of Stanley planes. Sharp is definitely the key. A set of water stones or diamond hones and a Veritas sharpening jig are very helpful. If you don't want to put out the money for stones then adhesive backed sandpaper in progressively finer grit is great. I use the sandpaper on a scrap piece of granite counter top.
There are a lot of great videos on using hand planes. David Charlesworth has some very good videos but you don't need to buy videos, Youtube has lots of good instructional videos.
How you sharpen a plane depends on how you intend to use it. If you are planing an edge, jointing is the term, then a straight blade is fine. If you are surfacing a board then you'll want to incorporate some camber into the blade edge. I use a Stanley 3, 4 or 4 1/2 for surfacing and a 5, 6, 7 or 8 for jointing.
I would use BLO over mineral oil as a finish unless you're doing a cutting board. Then use a food grade mineral oil. BLO will not give the hard finish of poly but is easy to touch up. I like it on my work bench surface.
