Never bought a wheelset before. Can you take the wheels right out of the box & put them on your bike to ride, or do they require any kind of truing before hand? Also is there any kind of sizing I should worry about? It says the hub is 8/9 speed compatible & I have 8 gears in the back so I'm good there. It's also disc & v-brake compatible, which will be good for when I put a disc brake up front but leave the v in the back. Just want to be informed before I buy & I know if I go to my LBS for advice they'll try to get me to buy from them. (which I do when I can, but I can't afford what they have as far as wheelsets)

It's ALWAYS a good idea to check the wheels for true -- after all, they've been in the hands of SHIPPERS (UPS, FedEx, USPS, etc.)!

I did the same thing for my sister's bike over the winter, and they didn't need any attention; I gave them the once-over anyway....

Hers what Id do. Put em on your bike. If theyre not true take em to LBS and have them true em. Also If the OL retailer is any good they'll give you some instruction on what to do. But Im a n00b so concider the source.

Yeah I want to start learning to true anyway, so probably what I'll do is wait until I have the money for the new wheels, then practice on my current wheelset (they're always slightly out of true, barely noticeable though) so that way if the new wheels have any imperfections I'll at least have any idea what to do. And then when I realize how much harder truing is than it seems, I can get fed up & take it to the LBS

Unless the shipping box looks like it had been through Grenada in 1983 then you are good to go! But truing is not a hard thing. I use to true road wheels and it is a piece of cake. Get a truing stand and begin to practice. As far as truing...............never seen a wheel yet that was 100% beyond a reasonable doubt perfectly and deniably true! That said.........you get them as close as you can.

Wheels can generally be run right out of the box, however...

1) Make sure the wheels came with rim tape (at least if you're running tires with tubes). Even if they come with plastic strips, I'd replace it with cloth tape like Velox.

2) People who want the wheels to last a long time will check the spoke tension and correct it if needed. This is more important than true, and attempting to true a new pair of wheels without taking tension into account can actually reduce the expected wheel life.

3) If they look horribly out of true, they probably got damaged in shipping and could have a shortened lifespan even if trued. I'd ask for a replacement if that happens, although wheels are usually shipped in a way that makes this unlikely.

I have never had a problem with online wheels. I always just put them on and started riding. Never had to retrue any yet (but they all are 32 spokes, but I have been up to 275lbs so they are a little stresssssed)
The XTR set did break a back spoke but I only noticed it when I was cleaning it and it was loose. The rim was not even 1mm out of true, and being a disk wheel I never noticed it.

First pair (about 6 years ago) were new Red Velocity Deep V rims on XT hubs 150 +25 shipping , I really liked the them so I thought online is the way to go (built by a guy in southern IL if I remember) .
Second pair (about 5 years ago) new Mavic 823 tubeless rims on XTR 960 centerlocks and XT rotors 249 + 30 shipping
Third pair (about 2 years ago) new Mavic open pro rims on Dura ace 7800 hubs 230 + 30 shipping (32 spoke bullet proof training wheels).
Forth pair (about 1 year ago) were used DT Swiss 4.1 rims on 240s centerlock hubs, for 220 + 30. They were used but had like 400 miles on them, basically like new.

And just recently I got a Powertap SL+ DISC hub with head unit on a Stans ZTS rim for 1100 shipped.

All were Ebay except the last was Craigslist. I have no worries about E-bay, but 1100 on CL did concern me a little.
But a few emails back on forth and everything checked out and went fine. I think online is the only way to go.