It took me 25 turns to get the mission done and have New Spain join me. By that time I could field some 2 and a half stacks. My fleet was very tiny consisting a small squadron of two galleons, a fifth or fourth rate and some light vessels. I was very lucky especially during my two wars with France. Development was slow but you need to upgrade those buildings. Once you start to expand the administrative taxes are going up so capturing more regions doesn't give you more money. From around 1725 / 1730 I was able to use my taxes to pay for my army (4.5 stacks) and navy (growing) and use the income from trade to pay for new buildings in my regions. By researching enlightenment techs you will get lower recruitment costs and lower upkeep.