The Wraith from Vegas intended for the message to reach Pegasus in his reality. Earth in that other reality stopped that, but an unintended rift was formed that allowed the message to spread to an unknown number of other realities.2) If the weak signal with the earth coordinates from the other reality was transmitted to one ship, wouldn't they have had it transmitted further so that it would not be only a single Wraith ship with the coordinates?
I may be wrong, but I don't believe the episode clarified whether that message was solely picked up by the super Hive or whether other Wraith in the galaxy also got the coordinates. The super Hive was the only one with the ability to act on it, but it's possible that the rest of the Wraith know where Earth is and now just need to work out a way to get there. Alternatively, it's possible that the signal was too weak to be picked up by typical Wraith sensors and thus only Earth and the super Hive (which, at that point, had sensors powerful enough to detect a cloaked jumper) received it.
I wouldn't be surprised if the signal was not at the same strength level across all the realities that it ended up being sent to, but rather was stronger in realities closer in proximity to the one it was sent from. What this means is that the main reality may be far enough away where only advanced sensors could pick it up, while other realities were not as lucky.
When the show was canceled they turned their plans for the first two episodes of season 6 into a movie script. Joseph Mallozzi gave an overview of the plot here: https://josephmallozzi.com/2013/03/3...on-and-beyond/3) What was the hypothetical future for a Season 6? What would happen to Todd? Who was the commander that did us the favor to resurrect Ronon, and what difference did it make how many humans were on board? Surely the ship was capable of tracking life signals.
Basically Todd would've been released back into the Pegasus galaxy by Sheppard.
The commander was played by the same actor who played Kenny. Given that Kenny was also one of Todd's underlings it would make sense that he was the one who betrayed Todd here. He's not named in the finale, though, and there's some dispute among fans whether the actor is playing a different Wraith character here. In short, actors frequently play different Wraith characters, that particular actor has played multiple Wraith, and Kenny has different prosthetic markings than Todd's underling from finale. So either they updated Kenny's prosthetic makeup or that was a Wraith we've never met before.
As to the number of humans issue; the Wraith have never been shown to have onboard sensors that can detect humans running around their ships. Either they don't have them at all or, more likely, they are not capable of distinguishing the difference between Wraith and human. Ancient sensors can do that, but Sheppard and co have a long history of remaining undetected (until they physically run into the Wraith) on their ships.
None. Again, the Vegas Wraith created an unintended rift that allowed the message he intended to send the Wraith in his reality to cross into an unknown number of other realities. The super Hive in the main reality happened to pick it up. That is all.4) What was supposed to be the relationship between "our" Wraith and the Wraith from one or more alternate realities?
I don't know, where was Lorne or Chuck? The writers picked what characters they wanted there. Paul McGillion was at one point a main cast member and he played an important role in that episode, so they had him stand there with the other main cast members and Ronon's girlfriend.5) If the Clone Beckett was able to stand looking at the Golden Gate Bridge, where was Radek?!