Wally West, the Flash, may be the self-proclaimed Fastest Man Alive, but he's officially stronger than Superman in one other important area. The Flash and Superman frequently race in DC Comics, and while Superman is incredibly fast, the Flash is arguably much faster.
Barry Allen is the current Flash in the comics, as well as the Flash in both the Arrowverse and the DCEU. He is certainly one of the fastest versions of the character and one of the most powerful. Barry can run faster than the speed of light and is a master in all forms of the Speed Force.
The Flash is NOT OP despite what you hear from a lot of fanboys. Superman, Wonder Woman, Captain Marvel/Shazam, and even Hawkman have proven to be able follow and react to his movements, Captain Atom can actually disrupt his connection to the speed force, and he would be NO MATCH for Aquaman underwater.
The group won't be listed on your profile, unless your friends are also in the group. However, you will be listed as a member of the group on the group page, and anyone with a Facebook account can see that list.
No, they will not receive a notification. Although there is no list of groups on someones profile, historically this information has not been private as group recommendations would be made in side panels of your Facebook feed showing which groups your friend were in.
Immediately. If it dies once, it will die again. Get your battery replaced and your charging system checked. If the battery is in good condition, a simple running of the engine for about 15 minutes will be enough to charge it up.