Being a avid crafter, I have had this question many times with friends that have experience with my new craft. Unfortunately, though some items stay in demand/high valued, not always are they worth the time to make compared to other easier and faster crafts with a lower profit margin.

The first thing to making money, is make sure to farm/craft your mats yourself. When you buy your materials, though it will be faster, it'll lower your profits (if any). Then pay attention to the Market Board (MB), it'll be a very big factor to your decision making. Sometimes a pair of crafters gloves is worth more than a spool of thread and easy to make. SO you can not only level Botanist, but also craft the mats into threads and gear for others to maximize the profit.

Botanist has a lot of uses for Cooking and Weaving, so pay attention to the indemand items for your level (if your not wanting to craft), so that you know what sells the most and has the highest profit margin.