Have a plan and enjoy the battle. Mike, I started playing tennis about 6 months ago. I seem to improve at a fairly rapid rate. Here is my dilemma. Here are a few thoughts.
Tennis is a skill sport where repetition is the key.
You need to make sure you are executing a stroke properly prior to practicing, or you will be reinforcing bad behavior. Lessons should certainly be considered. I suggest you consider group instruction. It is much more cost effective, plus it's an excellent way to meet people of a similar skill level. Finding others to play is always a challenge.