Hello, all!
I was looking for some help, and advice!

I've never been the GM of a game before, but I really have wanted to time and time again. Particularly, an RP based very much around solving challenges and the atmosphere of mystery.
If anyone has ever seen or played 999 (9 hours, 9 doors, 9 persons), there will be a fairly relatable scenario there, in which the game masters operate.
It's a DS game, by the way.

Anywho. I realise a self-insert character from the GM is often a bad idea in settings like this, unless it's a total NPC, or someone just doing the duty of announcing the next task to players.
Think Jigsaw from the first Saw movie. It's the only one I've seen, err...

I also realise it needs to be thought out from start to finish which is the hardest part.
Do you advise time markers? "Finish xyz before Thursday evening, for example, and let me know if there's an issue. I'll make extensions if necessary."
Or something like "For this section, everyone is allowed two posts minimum, and post 'done with this section' in the OOC when done for real"

And what are your opinions on restrictive GMing? Does it excite you? Does it drive you away?

And what are your tips to be a good GM in general?

Also, does one approve of elements of dice rolling in freeform settings? EG, if there is an actual battle between two players at a point, allowing dice rolls and predefined or mentioned stats to win it?
And if so, how do you know if someone's not lying to you on a roll?
Are there any dice rolling things that can be accessed by all the members of an RP for fair game and making it noteworthy that this person isn't lying? 
And if not, are we implementing it?
I hope so.

Much appreciated, thank you!
-Ginger