Drupal Developer Needed for Legacy E-Commerce Site

I am looking for a skilled Drupal developer (3+ years experience) who can update an older Drupal 7 website (Upgrade to see actual info) with a new mobile-friendly theme, optimize the site for improved speed, and also develop several new features and enhancements. Some new modules will need to be written or rewritten.

Experience with third party API's are also helpful, such as Paypal or Stripe for payment processing, Amazon S3 for file storage/delivery, Mautic (or possibly SendInBlue) for transactional email and marketing.

Project will be managed using Jira and Bitbucket, so experience with git repositories is required.

About the site:
Upgrade to see actual info offers stock music for businesses and video producers, and pays commission to artists for their music sold through the site. It was written 5-6 years ago in Drupal 7.

About the position:
You will be the only developer on this site, working directly with the site owners. This is a long-term position requiring a commitment of 10-20 hours per week (we are flexible). Pay is between USD $4-8/hour depending on skill and experience.

When applying, please answer the following questions:
1) What main things would you look at to speed up a Drupal website?
2) Describe your experience with writing custom Drupal modules.
3) Describe your experience working with 3rd party API's.
4) Why do you think you are a good fit for this particular job?
5) What questions do you have about this job?

Thank you,
Brandon