Something I noticed in the first scene is that when Fishlegs is looking at the map of where to search and it blows into his face, we see that it's the map Hiccup used to find Hamish's treasure.
But for some reason, he's reading the blank side!
Did Fishlegs draw the map on the blank side?
It was interesting to see Stoic has learned the finer points of dealing with dragons, since he calms Hookfang by emulating Hiccup.
It was also interesting to see that Hookfang will set himself on fire to act as a kind of emergency beacon, making himself highly visible in dim light.
Also, it was interesting to see a hint of "master swordsman Hiccup", because he uses the rod to fight like a sword!
However, at no time did I assume the Vikings are pulling their punches.
It's very clear that Astrid tried to kill Alvin in a previous episode (when you throw a axe directly at someone's head, that is intended to inflict a instant fatality!).
There was also a subtext that if pushed too far by Mildew, she will kill him without the slightest hint of remorse.
Likewise, Stoic was going to kill Dagar the Deranged (he is stopped 3 times) and it was only through the intervention of others that Dagar was not slain.
I did find it interesting that the Blacksmith shop has been dragon proofed, because when Toothless tries to enter, he can't get inside it.
I'm assuming the constant dragon attacks have forced the Outcasts to reinforce all their structures in this manner, for their own personal safety.
Still, in the long term, they won't really survive.
On a island where the inhabitants are powerful and out to attack you every moment you're outside, you won't last long.
And you can't stay inside your reinforced homes all the time, you have to hunt, get food and so on.
Essentially, everytime an Outcast goes outside, they're risking death and/or dragon attack.
As for the Dragons, I'm assuming they're not bothered by having other species of dragons around.
Their hostility is most likely a reaction to strangers, not an innate natural aggression to other creatures.
If you show you're not a threat, they're going to accept you being there.
Provided you're not dressed like an Outcast that is, I assume the Dragons are smart enough to recognize that any Outcast is a direct threat and will respond accordingly.
Crossbreeding I doubt is possible though, since they're so different to one another that genetic incompatibility would cause non-viable offspring.
At the very least, if the offspring survived, it would be badly malformed and would not live long.
At the other extreme, the genetic incompatiblity would cause the embryo to self terminate and the egg would be sterile.