Aero Tech you have asked a lot of questions there! I shall try to answer some of them.
Leak checks on items under the cowlings are done by motoring the engine over on the starter with the reverser cowls opened and fuel on. Called a wet cycle. This will find most leaks. You then close up and start the engine, leave it at idle for a time specified in the MM, shut it down, open the reverser cowls and check for leaks. If you have a leak that only apears at high power you do the same thing but obviously you have to run the engine at power!.
The MM will give you more information
You can open the fan cowls with the engine running to do a leak check. It is peferred that you start the engine with the cowls closed as the cowls are part of the fire containment area of the engine.(If you fire the fire bottles off with the cowls opened the extinguishing agent would blow away)
I would ONLY run an engine at idle with the cowls opened and I would not want anybody near the engine at above idle least of all me!
The red stripe indicates the danger area at idle ONLY and it is on the fan cowl
Safety straps are advisable but in my 28 years of engineering I have never seen one
Paint lines in the run bays? No
The manual start access point is within the danger area! Never done one and I don't want to do one either!!
I hope that will be of some use to you. Say a prayer for the guys that died and remember the desk sargent on Hill Street blues..
"Let's all be careful out there"
Rgds Dr I