1) Well, AFAIK you can't merge the POPs yourself. Secondly i'm not ready for wars right away, so i can't get the number of inhabitants down faster through wars than the regular growth.
2) I got my two cavalry division through an event. There is no brigade icon on the cavalry icon and they are called '1st cav. regular' and '2nd cav. regular', but i'm pretty sure it isn't a regular brigade.
And a new small question

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3) How much do the divisions in the mobilization pool cost a year? I was thinking about increasing that one to the point where i have 10 military points to become an independent nation. And how is it when you finally mobilize - does your relation with other nations go down or is the BB increased or how is it? I believe i have heard something about some negative things about mobilizing.