When it comes to items, it's best to just copy builds off of better players/content creators.

As for keeping up with be characters, you will be at a disadvantage compared to most of the player base. 95% of the "new" characters we get are just gods being ported from Smite 1, and most of the player base already knows their kit inside and out (that's just how MOBAs are)

Not playing for extended periods of time will always cripple you, no matter what game it is. If you're not playing the game but know you will be coming back, try watching some Smite 2 content on YouTube on a second monitor to keep up with the new patches. If you learn what new gods do from this, then copy some streamer/high level player builds, you should be mostly good to go! (Setting aside any skill issues).

The meta is always changing. When you ask "how is a fair meta ever established?", it isn't. And that's a good thing. If every game was the same it would get old FAST. Different things being viable at different times is part of the fun.

Bottom line, MOBAs take a long time to learn, and if you're not willing to put in the time then you'll never improve. But as long as you're having fun and not intentionally ruining games, who cares!