I finished the game once and I am thinking about going for the 100% the second time through, I want to know if all the strangers and freaks missions will be aviable after I do the main storyline missions.
It depends on what you mean by all the side stuff... I'm going to assume (ha, ha, funny joke there...) that you mean ALL the side stuff regardless of it's status in the chase to 100%...
There is (depending on a choice made late in the game) only one side thing (that I know of) that you cannot do once you progress past a certain point is:
a random Simeon mission. Go to the car dealership as either Michael or Franklin after the first heist but before Trevor is introduced to get it (this is what I hear anyway, as I've missed it and will check it out on my second playthru - I also hear it is but a small thing)...
I've wondered this too. I was saving as much of the side missions as I could for so I would have more to play in my sandbox once the story ended. I specifically saved Trevor's cause I actually liked playing him the most, who doesn't want a juggalo sidekick?
another question I have is, if I start a new game do I lose my current game? I've made a lot of progress in the game post story and don't want to lose that but I'd love to play through again with all the cut scenes and story lines rather than just load missions.