Sure, but if you're just starting out on YouTube it's very hard to ask someone to donate. Anyway, you can skip most ads after five seconds, and some ads can actually be quite interesting and have some significance. It's only when several ads start popping up unwarranted that I have a minor problem with.
Anyhow, I don't want to start a flame war either. Just my two cents.
Yes and no. You can use annonse for a (mostly) text based, static ad online, especially if it's found in an online newspaper or webzine, but I wouldn't use it for animated ads.
If you're refering to ads in a general sense, as in "There are too many ads on this website.", then you use "reklame".