It sounds like you're off to a good start with your lead generation. While it is important to keep lead volume strong, it's even more important to have a way to follow up with these leads and continue pushing them through your sales funnel until you can convert them into revenue. Without that follow-up, especially if you're generating leads through PPC, you're likely wasting the budget and energy you're putting toward your marketing efforts in the first place.
The first thing I'd recommend you do is create an automatic "kick-back" email that triggers as soon as a lead downloads your ebook. Be sure to thank them for downloading, give them a link to access the ebook, and then (most importantly) include your call-to-action for the next step you want them to take.
Second, figure out how you're going to handle these leads from a sales perspective. If you're stretched for bandwidth, I'd recommend a system where you assign dollar values to different types of leads, and only have a sales rep follow up with your highest value leads. How much is an ebook lead worth to your business? How much is a demo lead? What about someone who actively requests to be contacted?
You'll find that as you get these systems and processes underway, it'll be extremely useful to have a CRM system both for integrating with your marketing efforts and for helping your sales team to be able to sort and prioritize the leads they're reaching out to.
Lead conversion is a daily focus of mine in my role at HubSpot, and I'd be happy to chat further about how to get a strong marketing/sales funnel set up so you're better equipped to manage the leads you generate and better able to convert them into dollars. Let me know if there's anything I can do to help!