
First up there is case of sexual assault and a character having mental breakdown due to it. This happens in a single chapter of the story and was in no way shape or form was romanticized.
Second what Mizuki feels for Seima is purely idolization and admiration, that's more clear when we get to the finally part of the story. A big part of the story is Mizuki figuring that out and truly falling in love with the person thats been by his side. Yes the story could do more with it but it isn't bad by any means.
Oh yeah end note you can idolize someone but not be in love with them. that's fine.

So is it me or does it seem like he's doing the guy elves too? Like I'm cool with him being Bi. But yeah it seems like he's just have elf orgies along side the rest of the sex he's having.

He is! It's the same way in the light novel as well where he straight up says that he bangs them. He's completely impartial about sex or race. And so are all the other characters because he's not the only one doing the naked horizontal dance with those male elves. Believe me. Hell. Even the kobolds are in on this. I don't know why but it's so refreshing the way they don't differentiate.

You can find it up to a cer point on Japtem bit they dropped it.
http://japtem.com/projects/remonster-toc/
It's continued at Re:translation. You can basically see all the translated chapters at novel updates.
http://www.novelupdates.com/series/remonster/?pg=2
OKAY I'm gonna talk about this from someone more in the know. There will be a point where her skin color will be a minor plot point and it will piss people off.
First I will say it's less rasict on the part of the author and more Classist. Long story short whiter skin was a sign of nobility since they spent their time inside and while workers got dark from working in the fields and what not. And you can guess what they translated too over time, hell people with arker skin tend to be protrayed as country bumpkins or rebels sometimes depending on the work. It's still bad but not in the same way that rasicism is bad, just a different kind of awful.