Damage wise in starting my dawnguard playthrough and do they actually make an explosion when they hit a target or do they just make like a fiery blast sorta thing kinda like a firebolt

I think they explode on contact with anything, like a fireball.

It's a small blast and can't remember exact dmg but it's like 10 fire shock or frost + you can enchant the crossbows on top of the 50% ignored armor.

Yes they would be... if you could make them, for me I just dont like the idea of having 30 of each bolt. If you could, say at the forge, add a soul gem to the items needed to create a set of bolts then sure...

You can make them, it just takes the proper perks, & fire/frost/void salts to do so. I've crafted a few dozen of each.

They're okay. They'd don't do a whole lot of extra damage, but if you aim carefully you can hit several people.

WHAT! THANK YOU, I LOVE YOU!

No problem.
I believe you need Advanced Smithing for the steel bolts, & well. Dwarven Smithing, for the dwarven bolts.