1- If I buy the pack I have races every hour more or less like iRacing (againts humans)
Well, there is a multiplayer server browser where you can play against other people almost any time of the day. At night there are few people on though, so it may be tough to find a race.
Go into the MP server list now to see how many people are on. All of those servers are the ones people are driving on.
2- The pack is for ever and I dont need to pay more to play it? (I say this becuase in iRacing you must to pay the subscription to can play the content you bougth)
Correct. Once you buy a car, track, or pack... it is yours to keep, and you wont be charged more to use it. There is no subscription in RR. The only price you pay, is for the content you want. 1 time fee.
3- Is worth to buy this pack to start at this game?
That would be up to you and what you are comfortable spending... as well as what sort of cars interest you. The premium pack is easily the best value, but it is fairly expensive and comes with everything offered in the game. Which could mean it has cars or tracks you arent interested in.
My suggestion is to go to the store in game, look through all the cars, and test drive them. This way you can see what cars interests you.
From there, I would recommend
this guide to show you how to get the most content for your money. Basically, it includes buying vRP from the
RaceRoom Store and using that to buy the content in game. This way you will get a big discount if you buy a lot of vRP at once.
If you are only interested in the starter pack right now, I do think it is a good way to get a nice variety of content to use in the game. And you can always buy the premium pack later on if you find you enjoy the game and want to own more content. And later on, the premium pack would be discounted since you already own the starter pack.