Replacing or adding additional DB - what to consider?

Hi

My current home db is maxed out. 

I can either add a secondary db next to it or replace the db entirely. this is the home db which then links to inverter install in garage with its own inverter db / surge etc  

Im wanting some input on what to consider adding / leaving space for when doing the new db. 
 

- space for cbi astute or sonoff geyser controller for each geyser (1 or 2 breaker spaces allowed for each controller?)

- same for pool pump 

- surge protectors (how many and how much space)

- load / line voltage displays ? Necc or beneficial?

- space for sonoff or similar for outdoor lighting circuit so I can set up times for outdoor lights / control while away 

- a changeover switch to allow feed of inverter power to the nonessential side of db if necc 

- any other items to factor in with allowing space for

Trying to plan it out properly at the beginning so less of a mess when adding things in down the line 

any input appreciated!

thanks