I have a couple easy questions that I'm a little embarrassed to ask in public, but gonna do it anyway.

I have a Trek 3700 and need to do some chain maintenance. Can I just pop the chain off with a chain tool and then put the link back together, or would that ruin the link and I would have to replace it with a removable link? What removable link should I get if I need one?

Also, I looked into getting a replacement chain, but was quickly overwhelmed by the wide variety out there. I don't want to buy junk, but with a 3700 I'm obviously not looking for top of the line either. Which chain do I need for this thing? Or even what size do I need?

I don't have a LBS, otherwise I would go there to get my questions answered. I appreciate any assistance.

7 speed chain comes with masterlink.
https://www.nashbar.com/bikes/Product...1_10000_200291

You will need a chain tool to remove the old chain.

https://www.nashbar.com/bikes/Product...8_10000_200503

Whatever you do, don't ask how to clean a chain or what lube to use around here. bk

Assuming your chain doesn't have a master link, you can cut it but will need to buy a link to close it again. As far as what chain to buy, there are lots of nice inexpensive 7s (or 8s is OK too) chains available, many of which have a reusable connecting link. Buy a middle range chain, spending more might save some weight but won't get you more chain life.

Before buying a link for your current chain, measure it for stretch using a 12" ruler. Here's a link for instructions how, and about chains in general. You'll find Sheldon Brown's site handy for other things too.

why can't the link be reused? I always reuse them and have never had a problem. I don't trust master links, either.

Not true for most 6-7-8 speed chains. You should be able to reuse the pin, just make sure that the side plates are not distorted after reassembly and that the chain pivots smoothly at the pin. You may have to flex the joint slightly side to side to prevent it from binding.

All 9-speed and up chains (that I'm aware of) have swaged pins, where the outside diameter of the pin is expanded to hold the side plate in place. You can usually tell if the pins are swaged because there is a dimple in the center of the pin. These pins cannot be reused. For these chains, you must use a purpose-made replacement pin for that brand/size of chain, or a master link.

Since the OP has a 7-speed bike, I believe he should be able to break the chain (making sure the pin is not pushed completely out of the second side plate) and reassemble using the original pin. Alternatively, he can remove an outside link and replace with a master link. Personally, I always use a master link and I've never had any problems.