It completely changes the game
I always play standard size, not small and never Pangea. Maybe that’s a difference, especially the small.
Seville is an excellent city to keep.
Playing on deity, the barb camps are a killer because they are spawning a unit a turn, and a lot of units. Once a barb camp is triggered it is an ugly business, two or three make it just wreck your game when you had a good chance of taking Spain. You are doing the right thing, at least it looks that way, perhaps it is the way you fight? For example the archers on the left should now take 1 step backwards each not firing and the next turn take out one barb, the other will damage an archer but not kill it and will be damaged in return enough so you can kill that, The city on the right looks just fine… but more barbs come and when barb archers come it is just yuck.
I rarely get this situation (the camping, sure) so maybe it is my settings, maybe it is because I am paranoid about barb scouts.
I often do not worry about faith, I feel it makes it too easy. Playing without religion is my preference initially, later I will pillage faith and get lots of builders that way but initially, nah.
Population early is useful and chopping food early can speed your game up but most chopping you do want to wait for although there are plenty of exceptions like chopping in an extra horseman, if you are going to play with an army deck, you really should go all-in.
If you cannot play with two armies, I am not sure what to say, is that a mental block or a money issue?