k15n1

Really depends on what you are interested in doing with it... for biological samples (my bias) 5-20x is all the more you need. Beware of scopes that advertise large magnification. So many other things are more important---eye relief, for example. See if you can get one of those USB-enabled scopes with a camera built in. They look like toys but are actually pretty good.

platinum-catalyzed silicone may be an option.