Can sunblock be used as a effective moisturizer?

Not really. The fda has recommended that the term sunblock be dropped as it is often very misleading and can result in patients believing they have more protection from the sun than they actually do. I agree, a good sunscreen with an spf of 50, that contains both a uvb protector and a metal such as zinc or titanium oxide for uva. That's all you need but reapply it frequently. They are not good moisturizers.
Some. Moisturizer simply helps to lock moisture into the skin and protect it from drying out. Sunblock has chemical or physical uv blockers which protect the skin from the damaging rays of the sun. Some sunblocks/sunscreens are also moisturizing. You can look for a "moisturizing sunscreen" at your local pharmacy. Hope this helps!