Understanding data flow directions (pulling or pushing) and isolation of my Home Assistant instance

I am relatively new to HA, and currently developing a Hass.io solution on a nice little RPi 3 at home. I have a lot of research to do yet, but I am amazed at the power of this system so far.

I am looking for some guidance regarding flows of data to and from my Hass.io system. I have been reviewing notes in the forum and the guides, but I think I am missing a few details that will help me determine if my idea will work.

Currently my Hass.io system is isolated at home, behind my home firewall and unexposed to the Internet (which is exactly how I prefer it to remain). Integrating elements such as my LIFX lights, and my Nest and Plex devices work well, but I am just starting to dabble in services (such as GPS phone locations or Google) that rely on either the Cloud service or push/post calls directly to my Hass.io system.

It is still early days for me, so it is likely that I have missed some information, but I would greatly prefer to leverage a Linux hosting environment that I also have access to (complete with valid domain names, fixed ip’s and valid SSL certificates) to act as the “go-between” to my home system.

Ideally all “Internet” services that I may be interested in leveraging would contact my Internet facing server, and my home Hass.io system would pull information from that server periodically, thereby avoiding exposing my home system by ports or otherwise to the Internet.

My research so far seems to suggest that this can be a sensitive topic, so I would to re-affirm a few points:

  1. I am only doing research to see what is, and is not possible with the resources I have access to.
  2. I am not, at this time, considering any Alexa integration (which I am aware is a bit of a different animal)
  3. It is still early days for me understanding how the interconnections work with Hass.io and all the sensors and integration it supports, so if I misstep, it just means I am still learning and making mistakes.

Any guidance on good reference material on this type of topology would be greatly appreciated.

Thanks in advance.