Take a Lyra example project and check documentation on connecting it to EOS; Then try to do it. This will give you a good starting point of understanding of online features is UE.
From there, difference between using eos vs steam for matchmaking is literally the configuration file (albeit, ue’s support of steam really sucks: it may be unstable from one version of engine to another, so you may spend quite a time trying to make it work; Also ue support only most basic steam features like matchmaking, 80% of other are unimplemented)
Should note that in my steam-only project i dropped idea of using CommonUserPluging and gone for AdvancedSessionsSteam which is a good custom wrapper over engine’s features
I also am interested in getting data from players so need backend. I heard playfab or gamelift is fine for that.
Not quite getting your idea here, especially since i didn’t use playfab\gamelift myself. But you may specify which exactly you mean by “getting data from players”, so i can try explain it further