I've used it earlier and it calculates itself based on the days in the month. So, it does not default to 30 days and adjusts based on the days in the month (I believe it handles leap year as well). You can run a quick test to verify it before you automate it.
Unfortunately, this is not very well documented in SFMC guides.
If the personalization info you need is in an all subscribers attribute, you dont need it to be in the data extension, just use the personalization strings you indicated.
Personalization strings always check for a match on all subscribers profile attributes as well as the DE audience.
If they are not, you can use ampscript functions in the body of the email to pull from wherever the data is located.
Supposing that firstname is a column in a DE called 'subscribers', and that this DE has an 'emailaddress' column you could do this:
%%[
set @email = [email address]
set @firstname = Lookup('subscribers','firstname','emailaddress',@email)
]%%
This lookup function basically says return the value of firstname from the DE 'subscribers' where emailaddress equals this specific subscribers email address, then assign that value to @firstname.
To have it write to the html, instead of %%firstname%%, write:
%%=v(@firstname)=%%
Regarding your data filter question: I dont believe you can filter on tracking data with a data view without a solution like Audience builder.
You could, however, build a query activity and join in whatever columns were needed. This would return all the subscribers who meet your criteria:
select subscriberkey from _click
where jobid = 12345
where linkcontent like 'http://http://%'
From that point, you'd want to add an inner join, likely on subscriber key, to include whatever other columns you'd like in your sendable DE.
Best Answer
Try "greater than or equal to 0" in the filter for your measure - for some reason that has been much more reliable for me then the ">= 1" which is in documentation.