I'll be the bad guy here and say that you should not do a 10g tank. I understand that space can be limited and that restricts what you can have. A SW
tank requires a lot more then a FW
and if you are going to go with a 10 you may do better to start with a FW
tank until you can get a larger tank. With that said....
When you set up a tank that size you are going to need to do PWCs at least once a week and more likely 3-4 times a week, which means you are going to be mixing SW
up almost every day. Keeping the temp constant (one very very important aspect of a SW
tank) in a 10g is going to be tricky as that small amount of water will easily go up and down in temp based on room temp. With a 10g you will be limited to a couple of small fish and a shrimp or 2 as much more then that will quickly foul the water up. There are virtually no skimmer options for a 10g tank and skimming is an important part of keeping water clean. You will have to top off the water daily as it will evaporate quickly causing the SG
to rise and fall on a daily basis.
All of these factors are things that we all have to deal with in any size tank the difference being on a larger tank you have a lot more room for error. Starting out small can be done but it will require 100% commitment on your part. You wont be able to "let it go" for even a day as that could be the difference in your tank crashing or not...
I don't want to sound like a jerk here but I don't want you to go into a small tank blindly based solely on your friends knowledge!
Even if you were to go up to a 29g tank that would make things much easier and you are talking a few more inches of space taken up.
Sorry to sound so harsh and negative.....