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Django is rendering template from the database efficient

This is not a HOWTO question, as it, as such, has been answered before here
I am trying to integrate Django with modern frontend framework, and I found that it is possible to store and render Django templates from models. Since it is not a standard, I am wondering what are the advantages (or disadvantages if that's the case) of file based templates.
Reading though the documentation, I have seen that it is recommended to actually cache templates and models as much as possible for best performance, so why would it not be recommended to store templates in the database? It seems very convenient to me that in doing so pages can be edited from the admin panel (where you can add a code editor), which, along with the rest framework and a front end framework synergize very well.
From my research, the template tags and template language seem to work and the context can be passed in a view as well. the only thing I cannot figure out is the {include .. } tag, as it does not seem to point to a view. (although a custom tag cam be made to have this function)
Can such a setup be used in production? or are there security/performance/other concerns?

It's not recommended because templates are the developer's responsibility, not the site admin's.
Otherwise, there's not much performance difference between reading files directly from filesystem and from database.
One drawback of this approach is you don't get revision history (using git, mercurial etc). Sure, you can implement something similar to save the revisions in the database, but then why not use the better tools which already exist?
There's a Django flatpages app which lets you save HTML content in database. But the purpose of the app is to allow site admins to edit HTML content, such as information for an "About Us" page, because writing this info is not a developer's responsibility.

Templates on Django

I'm newbie on web dev and chose Django to start, in my application I need sign up and sign in freatures, searching i've found about django-registration:
Link to repo
The setting file and url are already configured, but I have to make the templates for login - I got some templates for test - but I have no idea where to put it, if I have to create a new app ("... startnewapp registration") or just create a directory for templates somewhere.
Can you help me?

you dont really need an external app for just a registration. it is simply one urlconf and one view.
but the most important thing for you now is to go through the tutorial, because tutorial tells you what to put where exactly.. and this cannot be explained here in 3 lines of text

Especially at the beginning it is very helpful to see an example where to put the things together. I developed a django-skeleton, which basically bootstraps a Django installation and boosts starting a new project. I also created views to use the builtin authentication module of Django for registration and to login: https://github.com/n2o/django-skeleton/
In this case I created a separate login app to modify the views and create my own templates.
This is not the easiest way to modify existing templates, but it fulfills all of my requirements.

Using custom forms in Django instead of modifying the source files

Let me preface this by saying I'm VERY new to Django and am also having a hard time with some of the documentation. I know that this question has surely been asked and answered a thousand times, but I can't seem to phrase my query properly.
I'm making a project that uses django-registration-redux, and I wanted to customize the template and the forms to accept additional user information. First, I noticed that my changes to the template files weren't having any effect , then I realized that it was using the template files from my Python install location instead of my actual project. I fixed this by setting the templates folder setting, but I also need to modify the registration-redux forms, and can't figure out how to override the default forms with local forms in my application.

You need not change the template settings for your existing project, but you have to make sure you have included 'registration' in the list of your INSTALLED_APPS. In the documentation its mentioned that
You can extend and customize the included templates as needed
Though its not very clear here, django registration redux is built on top of the in built django registration module. What you need to do is build your own custom registration form which is already explained in this answer.
In your case the template that you need to modify/extend is registration/registration_form.html.
Other useful resources that can help you:
http://www.tangowithdjango.com/book17/chapters/login_redux.html
https://www.youtube.com/watch?v=qkFWkOw-ByU

How do I create site homepage in Django that integrates multiple apps?

So I have been following along with the Django Tutorial and have successfully created multiple "apps" that I now want to start integrating into a holistic website (which in Django seems to be called a project).
So here are my questions:
How do I create a site homepage that is mostly static data (HTML, CSS, and images), but also includes data from some of the models of my projects?
How do I link from this homepage to my apps? So if I have an app called "polls" (as in the demo), would linking to the polls page be as simple as linking to /polls?

I think the general approach is that you also have to add one app which glues all your other apps together. So if you need a special homepage which somehow has to have full or part access to all the other apps you create an app for it and point for example your root url to this app.
Following that (and depending if your other apps share data with each other or not) its really as simple as you said. The polls app could be accessible under /polls as an example, depending on how you configured it in your urlconf etc.

Over-ride default Satchmo email with custom template

I'm using Satchmo for the shop section of a website. I'm trying to override the default 'order_complete' email with my own, but haven't been able to so far. The docs indicate that it should be done in the same way as overriding any other template. So I've created one in my template folder at shop/email/order_complete.html, but it isn't being picked up. Anyone have any ideas?

Just a guess but, is Satchmo listed in installed_apps before your own app? (If so the order_complete template may be being matched before yours is ever reached.)
Try moving your app before Satchmo and see if that solves it.

If you want your template folder to take precedence over the app template folders, you have to set your 'django.template.loaders.filesystem.load_template_source', before the app_directories loader.