I'm one of those out there who likes to just cruise on my longboard and get to where I'm going, but after seeing some videos I'm getting interested in trying to slide. Any tips and is it worth my time learning & buying some slide gear?
Longboarding is an exhilarating sport. I'm not going to lie, it can be a dangerous depending on the limits you are willing to reach within the sport. So if you really are interested and willing to test your limits, then yes it is worth your time and necessary for you to learn and equip yourself with the proper skills and gear. Tip #1: Wear a helmet :)
#1: Buy. A. Helmet. This piece of equipment is literally, a life saver. Its so much better knowing I can push my limits, and still be (sorta) safe because I have a helmet on.
And you're gonna want a stiff board for freeride, maybe a drop through board for beginner freeride. Depending on your budget, look into these companies: Rayne, Landyachtz, Sector 9, Loaded, and Bustin.
Find some reviews on some boards, and just pick what you think is best.
It depends. Longboarding is a really fun sport, but most of the tricks you see are learned from experience, not just picking it up right away. If you do enjoy longboarding then I say go for it! Like @ayedude693 said, the most important purchase will be a helmet.
Helmet and slide gloves are definitely needed like everyone said, I also recommend getting a slidey wheel such as Abec 11 freerides, Seismic Crybabbies or one of my new favorites 81a sugar mommas. Those with a stiff board should make it much simpler, there's also some good tip tricks you can look up. Also for learning have a wide open corner that you can see traffic so you don't get hit by a car.