As long as the image is exactly 100x100 and doesn't need to be resized when used as your avatar, it should remain transparent when uploaded. If I'm being honest I'm not really 100% sure, but I know with non-gif avatars, if you upload a transparent image that's bigger than the 100x100 default size, it'll resize to 100x100 and lose transparency, so I'm assuming the same applies to gifs.
There's also no need to bump up your questions when they were only asked ~3 hours ago. If it's been a few days and you've not received a response, then feel free to bump it. If it's only been a matter of hours then just leave it and someone will answer it eventually
It's pretty subjective, really. Like, if you're going to bump up someones shop which hasn't been posted in for a good 6 months, then obviously don't do it, but if you want to post in say, a video game thread, but the thread hasn't been posted in for a while (Super Pokemon Mystery Dungeon thread comes to mind), it'd be fine to bump that one up as long as you're still posting about the game and making it relevant.
Personally, if it's in the gaming boards/AC boards and as long as it's a general discussion thread, I think it's fine to bump it (obviously there are some exceptions) - if it's anywhere else like a shop, Brewster's, or question related, you should probably just remake the thread if it hasn't been active in the last 1-2 months. In saying that though, all staff members have different ideas of the world "relevant" (for example, if someone was to bump up a 3 year old thread in Brewster's such as "how often do you get hair curs" I would consider locking it - only because
I personally find it annoying - where as other staff members would leave it open since technically it's fine to bump up general discussion threads) so it really just depends.
It just comes down to your own common sense really. It shouldn't be too hard to factor out which threads are irrelevant and should be remade, and which ones are relevant and can be bumped up. If you're really that unsure, feel free to message a member of staff about it (linking the thread in question). Apple2012 also did a good job at describing what counts as relevant, too.
