No, don't be scared. Just realize there are consequences to everything we do and take responsibility for what happens rather than shrugging it off by saying "nature will take care of it". Just do the best ya can at keeping things "clean enough" (notice quotes
). Plants are completely fine.
I know Colleen has had great success with not keeping the pond "pristine clean" as the "experts" dictate.
You'll love this. "Back in the day" (at least hope folk don't believe it anymore)... the extremely avid koi "experts" would vacuum the roots of their plants and religiously do what they can to dispose of any decaying organics. Crazy, huh?
Decomposing organics can cause problems, but there are degrees to absolutely everything. Simply having plants are not going to cause unbelievable fish kills just as long as they do not suffocate the water and do not promote major bacterial problems, viral disease, parasites, and do not suck most of the oxygen out of the water. I know in some rivers Water Hyacinth is extremely invasive to the point of kill aquatic life. I have seen pictures of the plant covering entire rivers. To control it, there are hovercrafts with an aquatic surface shredder.
However, algae, when going crazy in a bloom, can cause serious problems.
Simply using skimmers and aerators will help you replenish the oxygen and they will help reduce any gas buildup from decaying organics. The main problem is the gas buildup from organic decomposition. You will receive maximum O2 saturation far before you expel the problematic gas build up. If you reduce the organics in your pond, then this becomes somewhat of a less problem. Water circulation, be it by pump flow or aerator, is very important especially during Winter, which I will probably get grief for saying that since it is highly debatable with very good points on both sides of the argument.
There are many types of tests for every type of water parameter out there. I would stick the particular manufacturers such as Tetra, Salifert, LaMotte, API, and SeaChem. Liquid kits tend to be more accurate than paper, but some parameters can only be tested by paper strips or a digital instrument. It all depends on how deep you want to get into testing stuff. Paper test strips and liquid kits can be more than enough that you will ever need.