1 - Instalar o i3-gaps

sudo apt install git libxcb1-dev libxcb-keysyms1-dev libpango1.0-dev libxcb-util0-dev libxcb-icccm4-dev libyajl-dev libstartup-notification0-dev libxcb-randr0-dev libev-dev libxcb-cursor-dev libxcb-xinerama0-dev libxcb-xkb-dev libxkbcommon-dev libxkbcommon-x11-dev autoconf libxcb-xrm0 libxcb-xrm-dev automake libxcb-shape0-dev -y && git clone https://www.github.com/Airblader/i3 i3-gaps && cd i3-gaps && autoreconf --force --install && rm -rf build/ && mkdir -p build && cd build/ && ../configure --prefix=/usr --sysconfdir=/etc --disable-sanitizers && make && sudo make install

Deslogar, alterar o display manager pra iniciar com o i3, e pressionar 2x enter pra criar os arquivos de configuração do i3 (se não conseguir deslogar via i3, deslogue via terminal).

2 - Instalar o Polybar

sudo apt-get install cmake cmake-data libcairo2-dev libxcb1-dev libxcb-ewmh-dev libxcb-icccm4-dev libxcb-image0-dev libxcb-randr0-dev libxcb-util0-dev libxcb-xkb-dev pkg-config python-xcbgen xcb-proto libxcb-xrm-dev libasound2-dev libmpdclient-dev libiw-dev libcurl4-openssl-dev libpulse-dev libxcb-composite0-dev xcb libxcb-ewmh2 -y && git clone https://github.com/jaagr/polybar.git && cd polybar && sudo ./build.sh

3 - Criar e configurar arquivos necessários

sudo chown -R $USER:$USER ~/.config/polybar && wget https://gitlab.com/terminalroot/popy/raw/master/launch.sh -O ~/.config/polybar/launch.sh && chmod +x ~/.config/polybar/launch.sh && echo -e 'for_window [class="^.*"] border pixel 0\ngaps inner 10\ngaps outer 2\nexec_always --no-startup-id $HOME/.config/polybar/launch.sh' >> ~/.config/i3/config

Deslogar e logar novamente.

4 - Instalar o Albert

sudo sh -c "echo 'deb http://download.opensuse.org/repositories/home:/manuelschneid3r/xUbuntu_18.04/ /' > /etc/apt/sources.list.d/home:manuelschneid3r.list" && wget -nv https://download.opensuse.org/repositories/home:manuelschneid3r/xUbuntu_18.04/Release.key -O Release.key && sudo apt-key add - < Release.key && sudo apt-get update && sudo apt-get install albert -y

Rode no terminal albert Configure o Hotkey, aplicativos, temas, …;
Abra o arquivo de configuração do i3 e comente a linha que contém dmenu: vi ~/.config/i3/config;
Adicione a linha albert & no final do arquivo: vi ~/.config/polybar/launch.sh;
Remova o alsa do painel do Polybar: vi ~/.config/polybar/config;
Reinicie o i3: Super + shift + r.

5 - Instalar o Cava

sudo apt-get install libfftw3-dev libasound2-dev libncursesw5-dev libpulse-dev libtool -y && wget http://ppa.launchpad.net/tehtotalpwnage/ppa/ubuntu/pool/main/c/cava/cava_0.6.0-0ubuntu3_amd64.deb && sudo dpkg -i cava*

Toque qualquer música (Youtube, por exemplo) e rode o cava: cava . Aplicativos recomendados: neofetch , scrot e mpg123. Você pode criar um aplicativo com Shell Script no seu Polybar e tocar as músicas que deseja, ex. (ao lado do volume):          .