First of all you are clearly ahead of most new pond owners - you know what questions to ask and have already produced more information than most experienced pond owners could do -
I have bought and owned a number of properties with ponds. Certainly not as informed as many experts on here but here is my advice - One....... do not over think it. Much of it is common sense - you clearly have too many trees around the pond that not only affect the water but also the ability to fish the place. Two ..... my advice is to pony up the money and get someone like Bob Lusk or someone he refers to come look at your pond and give you a game plan. You can spend a lot of $$ trying to figure it all out yourself or spend less money to have an expert come look at it - good luck to you