2: Yes, decelerations should cost a fate point every time.
No, they either require a Fate Point, or a successful skill roll. The example on page 116 bears this out, and the description of declarations on page 20 states that they can normally be done with a skill roll, but spending a fate point makes it certain and there's no need to make a roll.
And from page 196:
To make a declaration, state the aspect you wish to create or take advantage of. The GM assigns an appropriate difficulty, and you roll the appropriate skill. If you succeed, the fact is true and the aspect is immediately assigned to the target so that you can use it just as if you’d succeeded on an assessment roll.
A sticky aspect lasts until the person it is applied to makes a maneuver roll to remove it or until the end of a conflict or scene. The type of roll to get rid of an aspect depends on the aspect itself. 'Sloppy Fighting Technique' might just require a discipline roll to 'get back in the game', or it might stick with the thug through the whole fight.
It is a free action, but the GM has the power to veto it if the players start taking the mickey - remember that it's a tool to make the GM's job easier. If it starts making it harder then you need to talk to your players about appropriate uses of declarations. The use of a roll for declarations isn't actually an optional rule, except in the sense that when making a declaration you have the option to make a roll or spend a fate point.
And remember, if they fail a roll they may not realise it until too late.
"Hey, that thug has a sloppy fighting style! Leave him to me!"
"You know, I'm beginning to think that might be Drunken Monkey Kung Fu... I've never seen someone beaten into unconsciousness with their own fist before. Still, it sure did look like a sloppy fighting style from a distance. Maybe we should call an ambulance..."