Welcome Justin!
Another great source of used gear that no one every talks about (keeping it a secret?) is Ebay. Over the years I've used Ebay, I've bought tons of gear and saved tons of money. Buying anything used is tricky ... it helps to know it's true value and never forget shipping charges. I've even bought a bargain boat on Ebay. The Mamba 7.5 I bought last year was $400, had very little wear and even came with a like new skirt. I was prepared to pay $130 to motor freight it from RI, and still have a bargain (Mamba's are very popular so are very hard to find used, and even harder to find at a bargain price) but thanks to Jeff K & his Dad I got it delivered a week later with no freight charge

I also used to get a ton of bike gear on Ebay, and just last week saved over 50% on a set of cranks for the rear of one of my tandem bikes for Brit. For ski / snowboard gear for kids, you're crazy not to use Ebay. I can buy new / used gear for Brit in Summer and sell last season's outgrown gear back for the same price / more during the next winter (peak season, better selling price) making gear almost free!
Craig's list is trickier ... unfortunately I haven't found a way to nationwide search Craig's list, so you have to search city by city. I would do that for something hard to find used ... like a Mamba and actually found some there out West about the time I found the one I bought but they were more expensive. Also with Craig's you don't have the backup safety you have with Ebay ... you are definitely on your own there. Don't forget to regularly check with Southeastern outfitters for used / closeout gear. Canoe KY also sells they're demo boats at the end of season ... my All Star was a demo at CK.
For boats ... I'm very opinionated. I will recommend what I wish I had done when I got back into boating in '07 after taking 16 yrs off. I recommend getting a pseudo creeker / river runner to learn. Mamba, Diesel, Hero series in the appropriate size should be considered. You should paddle all of them in some Class II-III water before deciding. Later, if you feel up to it and have an intererest, I recommend adding a full on playboat. I sort of went the other way ... bought a Jackson Fun (pseudo playboat - river runner) then bought a full on creeker then later bought a full on playboat (All Star) and sold the Fun. The the Mamba type boat you will have an easy boat to roll, forgiving handling without much edge for easy learning, and and a good boat for learning creeking and big water in. They also surf well so they're good for learning to play. However, they are very hot / popular for a reason, so finding a used one won't be easy.
When it comes to buying other gear, used is fine except I would caution against a used PFD. They do lose flotation over time, so unless the seller will allow you to test the flotation before buying ... I would pay for a new one. Frequently there are good deals on new ones on Ebay, Sierra Trading Post and sales at various outfitters.
Finally I strongly recommend supporting Canoe KY when buying new gear that they can carry or order. They are good to us in supporting our winter roll sessions with boats - we make a good partnership.
Wes