Your team is good enough to start out with. Put Tiara as leader since all your other units are already different elements. You now have a rainbow team. for friends choose rainbow leaders like lodin, michelle, zelban, lilith etc and you will do fine.

For zel, weekend there is a zel dungeon in the vortex. You can do that for zel. Do not keep using low level rubbish units to level up your main team. You will run out of zel easily. Every day, go visit Randal (the green building) and collect your key. In the vortex there is a metal parade. Use the key to unlock. the units in  metal parade gives high XP.

U can try to mix n play on your team. So far all your team r attacker beside tiara. If u dun need a healer then u can change uda in.
N bout the bb lvling, my opinion is u evolve till 6* 1st only lvl up as every time u evolve it will reduce your bb by half