My entire method... In return for advice on how to scale

I was working full time for a company vetting applications for a certain type of job. It was a very desirable job/career and we were always on the lookout for new talent so by the time I left a few months ago I still had access to my company email address with about 2500 applications (email address, phone number, home address, age, etc). I figured there was some kind of way to monetise this and I'm quite knowledgeable on the industry so I wrote a short ebook about how to break into the industry. I put it on Kindle and figured I would make bank. I sent a bulk email to all on the list about how amazing the book was and over the next few days a steady stream of sales came through. But it wasn't exactly mind blowing or life changing, it was about the equivalent of working a 40 hour week in a normal job. And of course with Kindle I had to wait ages for them to pay me. It was anti climatic to say the least. Anyway I wanted to carry on selling the book because I was proud of it. So I posted ads on free sites like Starnow, Gumtree, etc pretending to be hiring for a job within the industry. After a couple days each ad has 20-30 responses and I send a brief message saying you have been selected for a telephone interview, to prepare i recommend you download this ebook. About 1 in 10 go to amazon and download. This has been a pretty consistent figure and isn't bad considering that you need a Kindle to download it. It's quite easy, it's a decent niche, a good book, and just a case of copying+pasting the ads and follow ups and you get a steady stream of Kindle income. Question is how can I grow this? Is it worth building a landing page with a pdf download and buying some adwords. Or something else? I'm quite new to IM so all thoughts appreciated and if you think it's a bit of a dickish thing to do then feel free to let me know as I kind of agree it's just I went to a lot of effort writing the book and wanna make something from it.

I feel that you're on the right track in terms of building mailing lists and such. You should try different ways to earn. Try out some CPA offers. Someone who went to vet school isn't going to buy an ebook reteaching them stuff.

Jesus.. Format your post, it's hard to read.

Yeah great method, thanks.

Anyway, if I was you I would just set up a website targeting that field/niche.
If you are knowledgeable then try to make it an authority site with great content.
Then you can either continue selling via Amazon or could consider Clickbank or just have it for sale on the site.

If that seems like hard work then just go with your landing page idea.

You and I have an entirely different idea of what "entire" means

Haha what else do you want?

I'd give you some scaling advice, but i'm not about to try a read that block text you just wrote.