Hi Bradbury,
It is likely to be the wood which is staining your water brown. Nothing to worry about really. You can get rid of the brown colour by water changes if you don't like it.
As for test kits, get a liquid test kit, not dip strips as these tend to be quite inaccurate. I'm not sure of the accuracy of the tablet test kits but liquid kits do the same job and are less hassle.
The tests you want to buy are PH, ammonia, nitrite and nitrate. You should be able to get a pack which includes all 4 tests.
Lots of people on here use API liquid test kit (Aquarium Pharmaceuticals) so they come recommended. I personally use Nutrafin liquid test kits but it's personal choice really.
I dont see that adding Filter Start to your tank will be of any benefit, and is just added expense. These products claim to contain the nitrifying bacteria which you need in your filter, although science suggests that they probably don't (The bacteria need a supply of flowing water to take oxygen from, and these solutions can't provide that). In my opinion, they are a waste of money. It is much cheaper and more reliable to build the bacteria up naturally which you will have done already if your tank has been running for a couple of years.
When you do your tests, ammonia and nitrite should both be 0. Any other result indicates a problem. Nitrate can safely be up to 100ppm, although testing your tap water is a good idea and aim to keep the nitrate reading in your tank similar to that from the tap. This is done through water changes.
There is no correct PH value and it depends what fish you have. A stable PH is much more important than having the correct value. Your PH is probably between 6 and 8 and anything in this range is fine, so long as it is stable (i cant stress that enough, PH fluctuations can be deadly for fish).
Hope this helps for now. Post your test results on here once you get your test kit and we'll be able to help you further.
Cheers
Backtotropical