1. The only time you have too many plants in your tank is when there is nowhere for the fish to swim.
2. You need pH, ammonia, nitrite and nitrate tests. Never use the Up and Down solutions that come with some kits. A basic pH is all you need, make sure it is for freshwater. A simple one is all you require, not one with the other chemicals included.
Ammonia, nitrite and nitrate kits seem to be around $20 - $25
You can also buy all in the one kit. Shop around as prices vary.
3. Testing during cycling is useful, or when something is wrong. Otherwise, I never test at all. If you are new to fishkeeping, testing before and after water changes, and recording the results, can be helpful.