They are called "supplements" for a reason – they are there to supplement an already quality diet. If you're already eating clean, healthy foods and get plenty of protein through meats, fish.etc then maybe it'll help you get in extra calories or whatever.
Whey protein isn't much different to chicken for example, it won't have any magic effect other than help you get more protein in. Creatine might have some benefit relevant to your goals, google it for some more information. Probably better you read it from the experts rather than us :P
The thing about creating causing water gain is true, but water weight is easily lost. Not a concern at all, unless you're in a sport where you need to meet a weight class. Heck, it varies so much naturally you probably don't even notice.