For the most part, it's "melee enemy to charge your staff". That's the whole thing. You can have seemingly endless staff charges as long as you mix in some melee. So maybe you put a few upgrades into good armor so you don't just die in melee. I find +4 Scale Armor to be sufficient for doing lots of melee.
I've had the most fun with a Staff of Magic Missiles. Each melee hit gives all of your wands 0.5 charges, and a zap from Magic Missile boosts all your wands to its level (as long as you actually hit an enemy with the zap.) So you kinda-sorta have an entire holster of wands equal to the level of your staff.
Normally, wands recharge at a rate relative to how many charges they're missing. Thats why a +8 wand goes from 0/10 charges to 1/10 very quickly, but a 0/2 wand takes a lot longer to get back a charge. With a Staff of MM, you just melee once and all your wands get 0.5 charges!
It's also kinda fun to imbue a Wand of Disintegration into a Projecting Staff. Then you can hit enemies 3 tiles away as if it were a whip. If you have a Ring of Arcana, it upgrades the staff's on-hit effect as if it were an enchantment. It will boost the reach from Disintegration just as much as it does the reach from Projecting. You can melee things across the room with a high enough ring!
Even without the ring, you can hit enemies around obstacles, so you can get the benefit of the extra reach even against ranged enemies as long as you can see the enemy. Perhaps with Eye of Newt, or you Metamorphose a tier 2 talent and get the Huntress' vision talent.
I don't remember what Wand of Blasting does for an on-hit effect. Wait, it's probably just "Elastic" and knocks away enemies. Either way, it's an excellent wand to put into your staff. I've had it to a high enough level that I can zap an enemy and push them 11 tiles, or zap one tile next to me and launch myself 11 tiles.
Blasting is an excellent Staff for Battlemage because even if you don't really want to melee, and you have 0 charges, you can hit an enemy just once to give it a charge and then blast that enemy across the room. (You just have to brace yourself against a wall before you zap an enemy in melee range or else you both go flying and you end up paralyzing yourself.) The damage from Wand of Blasting also gets very high at high levels.
In the end, you're still just a mage with a staff. You're not a warrior. You just have some tricks, more charges than normal, and a free weapon enchantment.
And like any mage, you absolutely duuuump upgrades into the staff. Ain't nothing wrong with a +19 staff. Although, a good ring might take some of those. I sometimes curse-infuse some armor if I feel too squishy. Preferably something that already had a couple upgrades.
