Good evening, Conneting filters in line or in paralel is not a solution and you won´t have any gain. Remember.. you always have the same power! One filter will not increase the power of the other. Simple as this. You may have a tiny tiny help by the OUTflow that will connect in the Inflow of the other but no reward will be achieved ... I believe you will have some issues by the time comes to clean them Now.. you say you have difficult to get good flow in all parts of the tank. Well this is quite vague.. what you mean precisely? Any tank has areas where there is less flow than other areas but that´s normal. Even if you put two filters one in each side of the tank you´ll never have the same flow in all tank. Of course that if your filter is not proper to the size of the tank you´ll have more issues. But has long as you have a proper filter and the IN / OUT well assembled (you should try your best combination for your layout) no issues will come along. As for light Nuno was testing for PAR measures and he acomplished that a PAR between 40 or 50 will do for any plant purpose. In other words use Medium Light.