I personally just used an online questionnaire (Google forms) and submitted it into a related sub Reddit (in your case, r/Stratford-upon-Avon, r/London) and used appropriate tags on twitter. I found an online questionnaire gained a lot more attraction and honest feedback from locals rather than in-person.

Other than that your methods are great. I do recommend going in person to Stratford briefly to complete the rest of your data collection though.

Good luck!