Im sorry fried rice, as I don't like to pick on anyone, but some of the info you're giving out is quite simply bad advice. I appreciate that you're trying to help out so please don't be discouraged and do keep posting, but you need to do some research and make sure you get your facts correct before you give people advise, particularly if you present it as fact as you have done. just a slight change of phrasing would help, instead of saying 'you can have ...' you can say, 'i think ... would be nice, not entirley sure if they are suitable though so do you're own research' or something like that to soften it a little. Sorry if that comes across as harsh but, particularly when giving out advice in the beginners forum, you should make sure you're facts are correct and the OP's often don't have the fishkeeping knowledge to be able to differentiate between which replies are good and which ones not so good.
OK, firstly, danio's are a no go for a 30l bio orb, for small fish they are incredibly active and need a lot of swimming room. tanks waaay too small for them.
cories do need to be kept in groups, a trio as a minimum, 6+ is better, while they may seem 'happy' (still swimming and eating) on their own, when you put them into a decent size group you really notice the difference and i can guarantee you wouldn't keep one singularly again. also witha bi-orb, the substrate is the filter, because it's so sharp it'll damage any bottom dwellers as they skate around on it, so bottom dwellers are a no go for bi orbs
the problem with tetra's and betta is not (in the case of most species) that the tetra's will pick on the betta but the other way around, simese fighting fish are not just called that for no reason, they may be small but they are highly aggressive fish and (although some individuals are the exception) will attack any fish which it deems to be a threat, so anything of a similar size, shape, highly colourful or with long fins is likely to be picked on..... this leaves v few options for tankmates for them so generally it's not advised to keep them as community fish.
there's a pinned topic with recommendations for stocking 10gal tanks, have a look in there for some inspiration.