1. When start new X App:
"Maximum number of clients reached"
Read by my lips carefully:
/etc/rc.d/rc.messagebus stop - for slack rc.dbus
If under KDE or X env must restart them some future is broken because dbus-daemon socket change ???
skype - Stupid Pyhon
ps ax | grep python
No need to kill will end alone when see that is not an loptop if it is not:
4177 ? S 0:00 /usr/bin/python /usr/bin/guidance-power-manager
kill 4177 - change PID
And all will be ok
2. Your USB keyboard is repeat pressed key very often and unnecessarily - my Logitech mx5000 have this problem and many other...
Go in System Settings - Keyboard - Enable Keyboard repeat - Disable or change Delay to Higher Value.
3. For GTK app use: lxappearance - to change Theme, Icons, fonts.