Minimum requirement of level 100, change job by the first npc you met when you get into the magic institute in Elban City.
Recommended build seems to be int dex vit or the auto attack enchanter build for utilising autoskill equipment.
It is recommended to level up your chasing, carpentry, smithing and alchemy production to a decent level (most seems to say 100). There are multiple recipes that create the alchemist's skill items and the higher level recipe not only require less items but also produce more skill item.
My suggestion would be to level up and go the wizard route, then go high wizard. That way you can utilize your hwiz aoe to level up your production. Also, i suggest you get some decent level before changing to alchemist (at least after you max both int and dex).
Based on the suggestions on the forum, alchemist may need 2 set of equipment. An autoskill set for farming items to make skill items and a casting/matk set for utilising skills.