Why is there a dependent limit for the amount of kids you can have on the active duty side and is this for all branches of the military?
I've never seen an answer in writing, but I'm guessing it has to do with raising a family on E-2/E-3 pay would create a major financial burden. I don't know if it affects all branches. Feel free to ask them.
I will be entering as an E-3 correct? If I manage to pick up PO-3 on the reserve side, is re-enlisting for Active Duty after my reserve (presuming I get in) contract feasible?
Yes, your prior service will qualify you for E-3. Going from Reserve to Active is nearly impossible right now. You'll have to serve as a Reservist for 2 years minimum before you can submit a request.
How long does it usually take for a reservist to get to boot camp after starting the whole recruiting process?
It depends on the individual, figure at least 6 months.