I've had some experience making basic missions for Flaming Cliffs a long time ago and though I might get back into it but have some questions:

Is there a guide somewhere explaining how to create a mission that has you do a troop pickup/drop off?

Can the Mi-8 perform the same role and in the mission building aspect does it work the same way?

Not really, but you effectively have 2 options which I'll try to explain...

1. There is a script in most of our missions called CTTS.lua. This script allows you to pickup / drop off troops or cargo using the in-game radio menu and is very effective.

To use it, you need to initialise the script in the triggers of a mission by creating a trigger that loads the script file, or by specifying it as the initialisation script, either will do.

Clients need to be given a specific group name 'helicargo1, 2, 3, etc'

Then you need to define the pickup areas for the troops and or cargo which are just trigger zones with a set name that is in the script ('pickzone1, 2, 3' I think).

Troops / cargo can then be dropped anywhere, or if you want to you can specify drop zones as well.

See this post on the ED Forums for a guide.

2. Using the in game - Embark - Disembark advanced waypoint actions for troops you can specify a location where troops will wait to be picked up using one of that units own waypoints (and the players radio menu). You then specify that units next waypoint where you want them dropped off and specify the advanced waypoint action as a 'Disembark' with a radius. If that group is then within the radius of the waypoint and the 'Transporting unit' is on the ground, they will get out and continue on their waypoint path.

You can set AI transports to pickup / drop off these troops as well with advanced waypoint actions if you wish.

Caveats:
1; a standard function in CTTS.lua that spawns units is broken in the latest 1.2.14 version of DCS and will crash the DCS game client when the player drops off troops.

2; The in-game 'Embark' 'Disembark' actions are overly complicated to setup and buggy. In my experience, the troops will quite often just run around in circles, physically run into the helicopters and die, or just stand still and refuse to move...

Any helicopter can perform these tasks, Mi-8, UH-1, it doesn't matter...

Good luck!

1; a standard function in CTTS.lua that spawns units is broken in the latest 1.2.14 version of DCS and will crash the DCS game client when the player drops off troops.

I thought I read in one of the release notes that this was fixed...can anyone confirm this? I am waiting for this to be fixed before I start anything

Fixed