Do you get to chose the order in which your units enter play when you do this tactic or do they all enter at the same time? (Can you resolve unit when entering effects in the order you want like if you put 2 dwarf cannon crews in play with this tactic would you only get to look at the top 5 for both dwarfs or would you get to do them one at a time)

You would get to choose everything since you are the one playing the action and you would be in control of all effects that come into play. To recap:

The units would all come in at the same time.

If you had 2 Dwarf Cannon Crews then their forced effects would go off at the same time. So, you would choose which order they would go off in. Since the Dwarf Cannon Crew says to shuffle your deck after your search, you would not have the same pool of cards when you resolve the second DCC effect.

would the dwarf cannon crew's effect happen and resolve before the epic spell put all the units in play basically going on the stack?

No.

The effect of the High Elf epic tactic would resolve first, putting all units into play. Then any forced effects that would happen at the same time (like 2 DCC coming in) would resolve in whatever order you want.

The units could not enter play before the HElf tactic resolved since it is that effect that puts them into play. Only after that entire tactic is resolved do the units enter play. Then any constants and then forced effects that would apply to units entering play would initiate/trigger. Each of those would resolve separately in the order determined by you..