How, if possible, can I log in to say, discuss.online above, with this account. Or do I need to make a second account over there.
You can view/comment/vote on all of the content there while logged into lemmy.world. As an example, you should be able to click this !flipperzero@programming.dev and participate there. or !AskUSA@discuss.online.
Also, related, is there a way to just, use my Mastodon account, and drop this one completely?
I am not a fan of “microblogging”, so I am not 100% certain. I have seen a lot of posts/comments from Mastodon on lemmy instances, they are the people using hashtags.
Kbin and Mbin are Lemmy-like systems that also hooks into microblogging much easier, so you might be able to do a one account thing there much easier.
Again, not certain because microblogging is not my jam.
Yep. He plays a much larger role in DISC