Blocking molotov throws probably would be done "OnPlayerRunCmd", but I'm kinda against it cause there are some specific situations where you really need throw a Molotov in these locations.
What I see some servers doing is blocking players to throw molotovs until they played for "X" time in the server or have X points (based on another points plugin system)
For button things usually, you achieve that by using "AcceptEntityInput" passing the entity as index and the Input. Like "Unlock" or "Trigger" ( e.g: AcceptEntityInput(entity, "Trigger"); ), of course every entity has a specific input you need do some research. (Valve wiki/Hammer, sometimes, is your friend)
Also in finale maps, some button actions like no mercy rooftop or parish bridge you need that all survivors are in "NAV" areas that are defined as "FINALE" (you can check with z_debug 1 in console, local server). Another point is that if you have stripper installed and do some "stripper_dump" you will notice that sometimes a lot of things are happening and is not just a button that you have to trigger.
Gonna say that the grouping area things are not easy to detect cause some use a "trigger_multiple" to check if all the survivors are in a specific place. (you can check my plugin
[L4D1 & L4D2] Trigger Multiple Ignore Incapacitated)
In saferoom I think there is another trigger that can tell you if you are in or out (you have to hook the input and manually set in a plugin variable that the client is in or out.
You could check left4dhooks which has a lot of useful natives and may give you some ready infos.
Probably other people will give you more information and ways to achieve that.
Wish you good luck.