People about Cosplay...
There’s a few things – one is that you you’re going to get asked for pictures, especially if you cosplay a popular character.
For conventions, make sure that you have a way of carrying essentials on you, even if your costume doesn’t have pockets. Perhaps make a simple bag to match your costume (same color as your outfit, or decorated with a suitable design, an example being a Jedi costume with the Jedi order symbol).
Wear your costume around before the convention, to make sure that you can move around in it, or that things don’t start slipping/pinching/falling apart after a little while. At home, there’s lots of time to make adjustments and fixes.
Don’t worry if you’re not as good as some of the veteran or professional cosplayers out there. Those cosplayers started somewhere too, and with practice, you too will eventually get good.
No, it is perfectly normal to buy a cosplay costume. Even professional cosplayers buy or get the costume made from someone else. However, making your own costume has a different thrill to it.
What is important though, is how you carry the costume and how much fun you’re having while cosplaying.
As for “devaluing someone’s participation” goes, some may feel that your cosplay is superior to them, when they took more efforts. However, it is not supposed to be that way as these things are done for fun.
Putting aside for the moment that the tone of the question doesn’t imply the most open of minds, cosplay is – simply – acting. Do you consider Mel Gibson, Ken Branagh, David Tennant, Cumberbatch, et. al. immature for wanting to dress up and act as Hamlet? Cosplay is a similar – if not identical – mindset: people, inspired by characters, possessing the right combination of talent, bravery and self-awareness, performing as said character for an audience. Whether it’s a convention stage or a Broadway stage makes no difference. The person who portrays Deadpool or Master Chief is very much spiritual kin to the person who plays King Lear or Hamlet. It’s wrong to praise one and denigrate the other based on the source of their inspiration, for to declare which works are “great” and which are not is subjective or worse. Still, even if most consider it blasphemy to compare Marvel to Shakespeare, the motivation to portray characters from either realm is identical and the healthy mindset WON’T criticize this, realizing that whatever it doesn’t “get” is not automatically inferior or invalid.
PS: Ironically you will find, if you but ask, that most cosplayers as children were very successful Trick or Treaters, as Halloween is quite often the “bug” that bites them for their subsequent motivation.