Hi

I am at level 12 there is still so much for me to do but when I get bored i like to move the main story along. Is it safe for me to complete the The House Always Wins and Ring-a-Ding-Ding quests without finishing the game?
What is the name of the last quest and at what point shuold I keep a save file before I am about to start it?

with as few spoilers as possible thanks for the help.

Yes

Hmm once you are sent to Hoover Dam, you're nearing the 'end'. Although there are at least a couple of quests left in the main quest, basically once you reach one of the following that is the last quest for each faction. No gods, No Masters; All or Nothing; Veni, Vidi, Vici; Eureka!.

cool thanks

The game has a huge popup notice saying "YOU ARE PASSING THE POINT OF NO RETURN" I believe you have the option to both save before you continue and the option of backing out. Once you've clicked the okay button there is no going back. So just play the game as you are already playing it with no fear.

Exactly. I believe the two options are "I'm ready" and "I'm not ready yet". Just pick the latter and you'll be fine. If you pick the former you will be "teleported" to the location where the quest starts, and you won't be able to fast travel. If you pick the latter, the box will go away and you have to talk to the person you got the previous quest from (Mr. House, Caesar, Yes Man or that NCR colonel lady) to get the box to pop back up and start the final quest.