The worst decision.
Why spend time and money to get a rating that won't even earn you minimum wage or pay your national insurance contribution?
The industry will not pay what instructors need let alone what they're worth.
You can spend a life time gaining the experience you need to instruct and still have wealthy individuals undermining your income because they have other income to prop up the low wages paid to instructors.
Try doing 400 hours a year and living on 12k. See if 600 hours is enough.
Instructing is the way to ruin. Live in a caravan on the airfield if your lucky and forget mortgages or renting proper accomodation.
You'll never earn enough to upgrade your ratings that's for sure. You're not even earning enough to renew your rating.
All your doing is subsidising wealthy students flight training while you live like a pauper.
Forget it. Get a job on a Tesco check out and earn far more for far less effort.
I've tried making it pay for 25 years in case your wondering.
You'd be better off busking in the high street with your dog.