Two ways with suit only - retrieve evidence (the guest talking to the manager won't mind you being there, the guard and the woman will) and either go through the right alley (if you do wait for the that annoying woman to stop speaking or through the restroom vent, down the laundry chute (or the stairs) beware of the janitor and the guards obviously, the electricians don't mind you are there. The electrician will "spot" you if he sees you calling the elevator. Disable fusebox. Call elevator. Hide in the back. If you went through the restroom, you have to hide from the janitor as well.

Two (maybe 3) ways to get the free janitor uniform - Sewers, vent where the electrician is standing in the water or through the restroom. Might even be doable if you wait for the janitor and the electrician to stop talking and go by the makeshift bridge or whatever it is. Bonus: you can activate the generator and fry the electrician standing in the water this way (just for fun). Haven't tested the last way. The rest is easy... You can also knock out the janitor that comes peeking down to the elevator below.

Distract the electrician on the right hand side by throwing a wrench, sprint to the wrench, pick it up, go back to the truck, subdue him once he goes around it. Go into the alley, so the guard starts the patrolling routine. Distract the guard that is not patrolling, drag the body to the dumpster, go into the hotel, up the stairs, call for the elevator (the electrician will spot you if he sees you, rest won't), retrieve the evidence (nobody will mind), enter the elevator.

One way with the free guard uniform (or two, haven't tested, just theorizing) - go either through the restroom vent or through the door the janitor goes through, and the window, wait for the guard routine and go through the door, pick up the uniform on the washing machines, go down the chute (can do it down the stairs as well) and the rest of the way is similar to the second way with suit-only.

I'll only outline the methods here (I usually pick up the film reel first):

1. Get the reel by going into the vent in the restroom (free janitor uniform in this room, though pretty useless I guess)
2. Keycard door - you can get keycards in 2 rooms with the guests or knocking out one of the maids in the room with the janitor uniform (all doable with suit only)
3. Through the window near the keycard door, distract the guard, watch out for the maid.
4. Through the police tape and activating the fire alarm, making the guards clear the stairs, argue in the lobby, allowing you to go upstairs.
5. Fire escape - I don't think this can be done unless you play the movie for the guards and for that you have to activate the fire alarm. Anyway, sabotage the speakers, wait for the guy to start repairing them (hide behind the desk) and go in the door, through the window. You can get the evidence this way, but only if you start the movie. Lots of trial and error.

Floor 8:

1. Bear route - either through the lobby (gotta wait for them to get called by the other guard) or through the window, distract the guard and go through it. I got the evidence just fine by going the window route, lobby route might require for you to start the projector.
2. Projector route - start the projector, wait for the guard by the desk to go inside the lobby (if you stand by him he'll rotate right always) go into the lobby and you can do the window route (useless I guess, it's shorter, faster and easier to go into the lobby and by the guard). Should be possible to get the evidence, haven't tried it.