Monster Grappling - fully explained

[Alveanerle]

Greetings and salutations!

While reading your extensive summary of grapple nuances, i could not help myself but notice some areas that are still a gray field for me. Could you please explain these a bit?
These are the questions, if i may:

- for improved grab grappling - what's the RAW reasoning behind doing grapple checks after the attack routine? Taking an example of a giant octopus, the improved grab part is written as follows:

To use this ability, a giant octopus must hit an opponent of any size with a tentacle attack. It can then attempt to start a grapple as a free action without provoking an attack of opportunity.

Doesn't the "it can then... as free action" mean that grapple check goes in just after the attack, disrupting the attack routine?

- what's the reasoning behind constrict attack damage being added to the normal unarmed/natural damage for grapple-to-damage checks in your examples? Taking the aforementioned giant octopus example, it goes as follows:

A giant octopus deals 2d8+6 points of damage with a successful grapple check.

Please note that there is no "in addition to the normal grapple check damage" part there anywhere. So should it be added or should it replace?
And if it gets added then should it be added to each grapple check, including the one to start grapple and other grapple checks or the one to move in grapple?

- how would you describe an attack routine of a giant octopus? 9 natural attacks, improved grab on 8 of those attacks, constrict, BAB +6, Grp +15.