Hi @Defalt and welcome to the Manjaro forum.
Firstly, after reading your post, I feel I must offer this link for consideration:
If after reading that, you still want to install Manjaro, this link covers many of the things you might encounter through the process:
I strongly recommend only having one OS per disk drive, even if multibooting. This is the safest and least troublesome configuration, despite those who would tell you otherwise. However, if you only have one disk, then choose which OS you prefer. If you wish to replace Linux Mint completely, the best option is to choose to use the full disk during installation. Calamares (the installer) will replace all partitions for you.
I would suggest using Plasma (as I do) or XFCE rather than i3WM, if your machine is capable enough. My opinion is that i3wm or Sway will prove difficult beasts to tame, given your level of Linux knowledge in general. If you need something lighter, Budgie or Cinnamon are worthwhile considerations.
Ultimately, the choice is up to you. Whatever you choose, make sure you have the latest available ISO file – if there is a choice between a full ISO and a Live ISO, choose full.
Here are more links that will help you use the forum more effectively to seek assistance when you need it; and you likely will need it.
Good luck.