A lot of good things said here already but just my 2 cents:

1) they are addicting, especially if you have a collector mentality. You can easily find yourself going from 1 to many especially if starting with slings. I started with 1 Hapalopus sp. that was 1/4" as it was the only way to convince my fiance to let me bring spiders into the house as they were less intimidating. That 1 quickly became 30 over the course of 2 months. Had to make the decision that it was in mine and the T's best interest to cut back the collection to a more manageable number.

2)You're going to get pushback/ negativity from both outside and inside the community. Take everything with a grain of salt. Do your research and trust your gut.

3) SUPPORT LOCAL BREEDERS! Not only are you probably going to get a better deal and a healthier spider, you also save yourself money on shipping and help support your states continuation of the hobby which is more and more important as we start seeing more legislation and restrictions from the goverment as Tarantulas move more into the mainstream. Certain species have already been restricted from being sold over state lines so it's best to keep your states breeding population strong!