question

Your AC system will need to be TT, so no neutral-earth bond and everything protected by an RCD somewhere. This is because the inverter can not supply sufficient current to trip even a fast MCB/RCBO quickly enough to be compliment.

1. Yes, just a single rod/grid of rods, to which all exposed metal parts are bonded.

2. There is no requirement to ground reference SELV circuits and a TT system isn't ground referenced anyway so NO. If you did want to ground reference the Neg of the DC you would have to use an isolated inverter to prevent that ground from being connected to the AC system by the inverter.

3. A single RCD and fuses/MCB's for individual circuits is a good plan. 500VA is a little under 2.2A, assuming the inverter is capable of twice that for a short period, starting a load or during an over current fault for example. Stuff you can touch, appliances that are plugged in, need to trip in less than 0.5 seconds in most cases, the RCD will handle that. Protecting a circuit from overcurrent with a fuse or MCB requires that you check the time trip curve of the protection device. Even the most sensitive MCB, a Type Z will require 2 X its rated current to trip quickly, in this application a 2A Type C, requiring at least 4 X rated current to trip, would probably never open rendering it useless and most 'standard fuses' are way worse than that.

Also make sure you use a DC capable RCD, the old standard AC RCD's are blind to, or even worse blinded by, DC currents, fault or otherwise, which means if the inverter was injecting any DC component on the AC circuit an AC RCD would not react to it and would likely stop reacting to AC leakage current because the DC current was interfering with it.

In general its a complex topic and one you need to look into properly before making a decision. There are still a lot of electricians getting this stuff wrong... There is good info on the likes of YouTube, and documentation all over the web, I hope my comments give you a basic grasp of the issues and a direction in which to start looking.

DO NOT use my limited comments as a design.

https://youtu.be/5WNAHhQEn9U?si=Ml8ZF58JFNXeJEWv RCD types and situations where DC injection is a BIG problem.

.....also this document from Victron is very useful and Chapter 7 refers to earthing/grounding
https://www.victronenergy.com/upload/documents/The_Wiring_Unlimited_book/43562-Wiring_Unlimited-pdf-en.pdf

That is very well explained! I will check the video and the book! Thank you!