Welcome to nsi!

1. is it ok to use all skill points on ranger skills, im planning to become an adventurer to wind walker

It is fine. It all depends on your favorable build, whether you want to be pvp based or pve based or a hybrid of both. You don't have to be restricted to your own class' skills. An example would be a shaman, which has a warlock's skills and a sage's skills in the first job. I'm a sorcerer and I took the heal skills that came with the first job in order to heal myself when needed.

2. what level and how can i change my job?

If I'm assuming correctly you mean going from an adventurer to a wind walker. The first job change is at level 30 and the second would be at level 75. Just open up your map and go to the NPC that corresponds to your class at that level, but it's Prince Shilly that gives you an option on what class to become first and directs you to that NPC. (If I remember correctly.) Then you are given a quest you must complete in order to become that class.

3. how can i regenerate fast? should i use lots of hp pots? (i keep running out of hp after several monsters)

Yes, hp pots help a lot. You should use them And also, your class has a regen skill as well, which regenerates a large amount of hp when used (careful though, because it has a long cd, so don't use it when you're good enough on hp).