AST should be the last person to rez. Should go SCH > WHM > AST/SMN. AST has the worst ways to regain MP of the healers, and if you have to rez people you will likely run into MP issues.

Keeping your Aspected Benefict HoT on the MT will go a long way to helping conserve mana. Your Benefic/Benefic II also cost less mana than the WHM/SCH's equivalent but at the cost of a bit of potency, but when you're just trying to top the MT off from 85-99% HP that's better since you won't be overhealing as much.

SCH/WHM have better ways to get the tank from low HP to full, so just throw your ED on them and maybe one Benefic II afterwards and keep using Benefic other than that. The other healer should really be the one doing most of the heavy emergency healing.

If you know there's going to be a single AoE hit, then start casting Aspected Helios early so it goes off right after the hit. The Heal + HoT will heal the party back to full so you don't have to use 2+ normal Helios to top off the party.

Find out the "tells" of the boss's stronger hits so you can start pre-casting Disable on bosses to get the 10% reduction from those hits. Over time that will save you and the other healer a small chunk of MP.

As for cards, I usually spread my first Spear/Ewer and save it for when I need to do some heavy healing or pop LA.

I'm only AST 52 but AST is basically a less potent 2.0 WHM minus Divine Seal/Benediction/Presence of Mind and I did get WHM to 50 in 2.0. These sorts of tips are what helped me conserve mana then so they should help now.