The sound of the sample is fine. The attack is the issue. It's the issue you'll run into with most live samples like that.
As for the cello getting out, that note should be right on a beat. If it's a grid based system that should work fine, but that might come back into the attack in the sample. There are a few times when the drums and cello don't quite synch up properly, presumably for the same reason.
Not having and end goal kind of shows
If you're not taking this super-seriously then it's fine. The AO soundtrack is really fantastic in the way it takes one or two rhythmic ideas and builds the soundtrack of an entire area around them. It's very hard to work with in an arranging sense. Tackling some more original stuff in a similar style is probably has a lot more potential.
As far as the 5ths go apparently my pitching sucks today. Sorry. Either way it's not really clear that you're using 5ths, and it doesn't really add anything like what an open 5th could.
In regards to the intro music, what about people who have never visited your channel before? It's all well and good to cater to regulars, but ideally most of your videos should be clear and approachable to newcomers. I'll probably listen to any music stuff you post here, but I'm unlikely to ever watch anything else on your channel. The idea of musical stuff is a good draw for people.