Your sales funnel is healthy if you have enough prospects going through it. If you’re moving enough prospects through the funnel with the experiences and interactions you create and if you are able to profitably convert enough prospects into paying customers, your sales funnel is healthy. See our article on Sales Metrics – 17 Reports That Improve Your Sales Pipeline Performance to help measure your sales funnel health.
Prospecting and marketing are all the things you do to get people into the first of your sales funnel stages. Note that stages are broken into two or more steps wherever possible. A demo could be called a single stage, but in real life it involves a lot of things: contacting the customer, sending reminders, doing the demo, and then following up. Whatever your own sales stages look like, the support you need in managing them will be the same.