Hey Girl-
Sorry I didn't reply sooner... so basically Salys hair extensions don't have a good reputation. They are the cheepest you can get I think, or close to that.
You want to look for one thing if you're looking for hair extensions, it is remy hair. Cuticle aligned. When you don't see that mentioned, forget it. Unless you go for a short term install, or just want to practice on some non expensive hair at first, or plan on making clip in that you'll wear every once in a while.
If you want to live with the extensions, wash them on a regular basis, style them with heat tools etc. then you need a minimum of quality or honestly it is a waste of money. You'll end uo with ugly looking hair, all tangled up after a few shampoos. We've almost all made that mistake.
If you re looking for dark colors, then you can get some great indian hair, that is not always crazy expensive.
I prefer asian type of hair like Bohyme personally.
As for maintenance, you'll learn your way. I love Pantene products so unlike Sinful Girl I would totally recommend them. Clarifying poo every once in a while gets rid of any ocasional build up, if need be.
Silicone serum, smoothing products, conditioning and deep conditioning are a must.
Owning a good straight iron can be a life saver too when your hair gets a bit dry.
If you want recommendations for not too expensive but decent quality hair, you should read read read. Spend hours on the hair extensions forum, you'll find tons of info.
Some girls have posted good reviews of hair that wasn't so expensive. I can't remember names right about now, but definitely go on the hunt and dig out old posts!
Good luck!