What do you think about it? Is the Federation something that modern, real Marxists should strive for?
It can't hurt to have dreams and aspirations. It may not be possible to do many of the things the federation shows being done technology wise such as colonizing and reaching out to the stars beyond out solar system (I mean maybe you could build colony ships with robots, frozen eggs and sperm, artificial wombs and send them on a several hundred or thousand year journey to other solar systems and inhabitable planets to colonize them but it'd be entirely different than what Star Trek shows and they'd be effectively cut off from us and us from them) but it does show the better world/galaxy if we work cooperatively idea well.
As to striving for it? It's not something within reach of any of our lifetimes. It isn't really our purview to strive for it, it would be the job of those who come after us or after those to do that.
If you're asking if it's the type of fiction I like seeing and think we as socialists should encourage them absolutely, 100%. And yes by the way, new Trek is liberal garbage because they couldn't stand seeing socialists winning. Any Trek revival under socialism will retcon everything after DS9 and the TNG movies.
Are the ideals of the Federation compatible with the ideas of communism?
Most of them. Although I've watched all old Trek I'm not a scholar on it or a total lore nerd so someone else might better chime in. I'm sure there are problems here and there as it isn't like Roddenberry had a warehouse full of blackmail on CBS executives and the government to allow him to do whatever he wanted perfectly (though I do love the story about how they wanted to put a preacher on the original enterprise as part of the bridge crew and every time he'd just say "interesting idea" and walk off looking thoughtful).