If I subscribe this month to ps plus will I get access to all free games from the beggining of the service ?
No you will not, unfortunatly. Which from a business and senority standpoint, makes sense, the longer you have the service, the more stuff you will have.
Amazon and Gamestop(maybe Newegg too) had Playstation Plus for 30 bucks. THIS is the time to get the Subscriptions.
The three instant games on the Playstation Vita have remained since it became available on the Vita, but there's still a half dozen solid titles you missed out on.
I download everything free, even if I have no desire to play it, because either someone else might, or I might get to it one day and check it out because that person is curious about it.