Here's a link that will tell you more about AA http://eq2.zam.com/wiki/Alternate_Advancements_%28EQ2%29
Also, the amount you should have at any given level is always up for debate, depending on who you talk to. Some people swear by leveling up as fast as you can and then getting AA, others will remain level 20 for months, gaining as many AA as they can. I tend to fall in the middle of these camps. I focus on AA for a while until the quests start to outlevel me, then I focus on levels for a while until the levels of my quests start dropping, rinse and repeat.
The best way to upgrade your spells is to look on the broker for them. The order is Apprentice > Journeyman > Adept > Expert > Master. You get App. free (as you know), players can make Journeyman and Expert spells, and Adepts and Masters are drops. If you're not able to find anyone selling the upgrade you need, usually asking in general chat for someone to make one for you will work, especially if you say you're providing the harvests.
There is also spell researching. Open your Knowledge book (hit K) and the far right tab says Research. At level 20, you can start researching your spell upgrades free. The lower levels take just a few hours and the higher you get, the longer it takes. At level cap, spells that are anywhere between level 85-90 can take about a month to research. But it's one other option for you to get your upgrades.