For the action bar position, there should be a settings window for the action bars (esc -> settings/interface -> actions bars tab. don't have exact names as i am not ingame atm, but that should be it). change the action bar width from 1 to however wide you want it, and then put the # of buttons to what you want. you can have a total of 20 buttons per bar, with any width (for example, a 20 action action bar at 2 width gives you 2 columns of 10 buttons, at 3 width it gives you 2 columns of 7 and a column of 6).
as for the chat window, you should be able to move it first right clicking the "general" tab title and then unselecting "lock tab". then just drag it where you want.
as for resizing, the best option i found was to go into the video settings (esc -> audio/video) and check the "ui scaling" feature.
somebody else can probably give better recommendations, particularly if you'd like any sort of ui overhaul addons.