Actually having 1 relatively big (not 1k) capitalist pop only for the whole nation when you start the game with a relatively poor country can be the most efficient option for a few reasons.
-First if you have more capitalist pops they need to share the rich pop income with more other capitalists, decreasing their income per pop and increasing their demand for goods reducing the speed by which the cash-reserves they have grow, reducing speed of factory/railroad building
-Second, factories in the begin of the game aren't extremely profitable if you don't have a good infrastructure, so it might be best to make sure the capitalists are mostly building railroads. When you have more states with a capitalist, relatively more money will be spent on building factories and less on railroads.
-Also keep in mind that railroads will (almost) always increase your income (and so also the income for your capitalists) from RGO's and increase efficiency for factories so these are best in the start of the game
-Also if you haven't invented some factories, capitalists will still try to built them, losing money for no factories. So more capitalists building factories will result in losing more money.
Still there could be reasons to make more than 1 capitalist:
-If you have aristocrats in your country and you can't or don't want to tax them to death, it might be useful to increase the amount of capitalists to increase their share of the rich-income
Of course this doesn't apply as much to the late-game