Firmware updates seem to be at least every 2 weeks, they always have the vague "improve performance" , sony clearly dont want to display the actual changelogs, but most are likely anti piracy related. If you dont update then you cannot login to PSN which means no online gaming, no game or patch downloads, and no trophy sync. But the firmware updates are small.
Game patches depends on the game, FF15 has patches at least once a month and they often very large, usually several gigs. However other games can go without patches for months and be much smaller size. Games usually lockout online functionality if they not on latest patch.
Patches used to be fully automated for all games, so when you played a game the chances are it would be patched up, but sony made a change to make it only do the most recent games you played to save them bandwidth costs. Even for psn+ members.
PS4 base games all work on the PS4 pro. IT even has a boost mode you can turn on which cranks the cpu clock to 2.1ghz on PS4 base games which will make them run faster if they cpu bound (Which many are).
PS4 pro has 5ghz wifi whilst PS4 base only has 2.4. but ps4 slim also has the 5ghz wifi.
Comes with HDMI cable so any HDMI monitor will work.
Also if you connect a controller with a cable it will actually be a wired connection so no need to worry about bluetooth sync issues, on the base PS4, it stayed using bluetooth when connected via cable.