I like these suggestions.
Mechanic App
The Ability to select what is needed is a great suggestion. The number of times I've arrived at an MR and had to change the vehicle because they needed their vehicle to be flipped/towed becomes more common than not. WE NEED THIS.
As an additional feature, though it might seem unpopular, I believe the ability of Management members to cease services for some time when no Mechanics are available, i.e General Staff Meetings, events, etc. The reason I suggest this is because in the past players would spam MRs despite Mechanics being unavailable due to meetings, events, etc, I understand why though since it says 'x Mechanics are online'. If there could be a way to combat the spam of MRs during these times, it'd be great.
Barriers/Cones
I love this idea, it creates much more immersion and can be a reason to give additional training to Mechanics.
Deny Mech Request
I can see this one being useful, however, depending on the shop there could be different reasons to deny it. For example, if LSC denies it for 'you're blacklisted', would this also cancel it for Benny's and Bayview? Perhaps the Mechanic app could have the option to select the Mechanic Shop you want to receive a service from, as well as how many Mechanics are online for said Mechanic Shop.
Vehicles under 300
Yes, need.
Vehicle Blips
Yes.
Incident clean-ups
Yeah, gimme more to do, I want it. I already see Mechanics doing cleaning RP so to have an actual scripted event just gives more immersion. As for scripted towing, I believe this should only happen when a certain number of Mechs are online. Don't want mechs to abandon the shop or player MRs for a scripted event.
Order System
I believe with some testing as well as procedure changes, this would be viable.
New /mechoffer command with no base price
This I can see being useful when the game bugs out and doesn't apply mods/repair, as for towing, afaik (at least in LSCs case) no Mechanic shop charges for towing. Having the option would be welcomed though.
Temp Keys
Ya!
Overall I like the ideas, Denji Deveel out.