You can get in touch with other Plumi developers via the Plumi blog which has information on email lists, the Plumi IRC channel and a contact form to send an email directly to the project maintainers. We can't always solve your problem, but should always be able to offer some advice or direct you to other people who may be able to help.
It's always best to browse through the issue tracker before asking a question, as this lists known issues and feature requests.
If your query relates to customisation beyond Plumi itself, you can also visit the Plone chat rooms or support forums if you have more specific questions. Or learn how to design, build, and deploy a website in Plone through one of the numerous Plone training sessions around the world.