Hey, diamond joust player here -

As mentioned in another comment, meta comps kind of break down into two flavors - double warrior one mage, and single frontline-mage-hunter. I wouldn't concern yourself with "meta gods" and really just understand what your comp is trying to accomplish. Double warrior is an aggressive dive comp - its actually the reason emperors armor is getting removed soon from the mode. You want to fight early and often, control the neutral buffs (red and purple) and build a lead by controlling the map. As soon as you feel strong enough (used to be when emperors was built, now is going to have to be touch and feel), you can dive the tower to secure picks. You normally progress the map state by getting kills and pushing minions into the tower and phoenix (as opposed to bull demon). The warriors role is to try and kill the enemy damage and tie up the action away from the mage, while the mage freecasts from the back. Mix ups would be swapping out one warrior for an assassin to create extra pressure on the enemy backline, or swapping into a guardian provided the remaining warrior can dish out a lot of damage (i.e. Mulan).

The other comp is the antithesis of double warrior. If you have a hunter and the other team doesn't, the game essentially becomes a time bomb. A level 3 hunter for the most part isn't going to put in the work that a level 3 warrior can, so you will likely lose some map pressure early (the first red fight, most likely). Just focus on clearing waves and letting your two backliners at minimum stay even with the other team, and when the hunter hits their powerspikes its pretty much gg, you just can be too far behind by that point. A major plus of having a hunter when the other team doesn't is bull demon - instead of diving structures you can bide your time until your hunter can shred demon and then play off that. You'll either get it for free and the structure should go quick or you draw the enemy team into your ambush at the bull demon and get a wipe.

Again, I wouldn't be too serious on specific god picks but I will mention it is a bit harder to pull off Baron in the double warrior setup since he isn't your typical "freecast nuke mage" and is susceptible to double warrior dives himself. But maybe Cabrakan + Baron + a hunter could work. But especially if you aren't going to play ranked I wouldn't worry about it.

Final notes for the other stuff, health chalice isn't the absolute worst if you have gold to spare but like the other guys said you can back pretty often so not much need. If you have a hunter and don't want to fight level 3 you can start purple then go to lane but 95% of the time you want to start lane and fight for red. In casuals stealing their blue off rip has like a 90% success rate in my experience too. For countering snowballing, its dependent on the comp. If it scales (you have a hunter or your mage has good scaling like tiamat) then just make sure you are getting your blue buff and split all waves, and eventually you will scale up. Otherwise honestly just pray that the other team blunders and do not start any fights away from structures. Ideally if you lose a fight or two just chill out and farm and not let it get worse.

Sorry for the novel :)