Programming like a pro: tools for software planning

[BigMan]

Hi,

in the past I used Python mainly for some small applications (all for private purposes).
Now I have something bigger in mind (a kind of home-automation) and I would like to do it a bit more professional.

So far I started coding always "straight away". But now I want to think in advance, how the software-structure/architecture could look like, which releases I should have, etc.
Indeed, I was close to start just by using Libre-Office Write/Impress for this ... but I am wondering: isn't there something in the open-software-world more specialized for this 

(I am running Arch Linux, Python3, and my editor is Geany)

Thanks in advance for all hints and tips

[Ofnuts]

In the professional world, these things happen in three stages:

1. Requirements are defined. This is plain text and some tables so your best tool is an Office Suite
   
2. The "architects" size the required hardware, figure out which software will be used, design the data model (which in most cases is tightly coupled to the database structure). A good deal of this is often done using UML. There are modeling tools that will also produce the DDL (SQL scripts to create the database tables), and stubs for the main classes.
   
3. Developers write the code (using IDEs).