There's two main tyoe of needles and they have like 50 different names but I prefer the normal style for smaller twine but I prefer the H style for larger stuff like 550 cord.
Anyhow I order all my stuff now from the fish net company in Jonesville Lousinia,their shipping is kinda expensive but their service is beyond amazing ! Actually made an order then had one of the clerk's call the next day and said he saw my order and figured what I was as making and told me what I ordered wasn't what I actually wanted and gave me the correct poportions and even saved me some $$$. Jannsnetcraft is good too but they seem a lil more pricy and less selection.
So if you order from the fish net company what I used is called a Duro needle and my favorite is like a medium size I reckon. Though I'm starting to like their super star 8 a bit more though,though it can be a pain when starting the fist set of meshes due to it's size.



Now good thing about janns is you can order a whole basic set of needles if you want.

Now as far as twine I'mma go ahead and save you a massive migraine and tell you to stay faaaaar away from Mason twine and that bank line crap from Wally world. It's tared uneven and it's twist is loose and crappy at best, it will work but it's not something I wanna work with if I had a choice.
What I use now is the Superbrand twine that the fish net company stocks. Now they have alot of different kinds but the bonded green and black tarred is what I've deleted with and I like both. The bonded has kinda a slight waxy type coating that helps it keep knots from slipping like Mason twine will. It's also real nice in your hands . I have a few knots slip but how ever but not enough that I'd consider it a problem. It's just great to work with in general.
Their tarred twine is great as well. If you check out the cheaper crap you find it often has globbing and "zebra striping" where the tar didn't. Coat well and this can caun bad knot holding,that being said it "will" work. But the mighty brand has a wonderful even coating. It's a little on the stiff side so your gonna need to put the ole man hands on it when you tie you knots but once that tar bonds and works a little those knots will be like concrete. The tarred twine can be a little round on the hands at times though.
As far a sizes your gonna get alot of different things. For fish most will recommend size ,#9-12 and turtles 15-18. Personally from the snappers in the 10-30 lbs range I've messed with #15 is about perfect for me.that being said for much areger ones or for trap your gonna work all the time #18 won't hurt a thing. In fact I thing beaverfoot who makes some of the best D style hoop nets around uses #18 last time I checkeded and ive never heard a bad thing about his nets !