web app questions-data encryption and cost of data storage

Hi, I have been making a web application that runs with MAMP, and I am thinking of making it available on the real web (not just with MAMP), so that users can use it on other devices.

It is an app that stores a lot of data entered by the user. It uses PHP and MySQL.

Does Treehouse or anywhere else have any info on getting a web app started on the web? Specifically, I am wondering about the following:

Security

It's a bit daunting being responsible for people's data. I haven’t come across much about protecting data on Treehouse, but I suppose there would be things I should know about how to protect it from the internet villains out there.

For example, I remember getting emails from apps I was using earlier this year telling me to change my passwords due to the Heartbleed Bug. So I figure if I create an app I should be responsible for knowing about the security issues out there and protecting users from them. But I don’t know how I would do this. I feel like there should be some course on the topic.

I notice that other web apps tend to have fancy jargon regarding the security of their data, so I figure maybe I should learn how to apply the same sort of security for my app. For example,

Dropbox 'secures your files with 256-bit AES encryption’.

1Password has 'AES-256 using Encrypt-then-MAC’ and 'GPU resistant PBKDF2-HMAC-SHA512’.

Basically, could you share any tips or resources please about how to protect my users’ data or anything else I should know about security? Does treehouse have anything about this?

Financially

Currently, the only web host I’ve used is Web Hosting for Students. I’m guessing I wouldn’t be able to store enough data with them and so maybe I’d have to go with a more expensive web host. I’m wondering how other web apps like Evernote, Dropbox, or Workflowy were able to get started financially while still allowing their users to use their apps for free, and especially when the free limit of storage space is reset each month! Can anyone explain please how I could make my app free to use when I imagine the data storage could get quite expensive? I know the other apps have paid subscriptions as well as the free ones, but I’m thinking people may not want to pay for my app in the early stages.