Questions regarding updating to 4.30 from 3.55

1. I have like 50 games on my 3.55 kmeaw ps3. Some are patched to work on 3.55, some are not. Will these games all work perfectly when i upgrade to 4.30?

2. Also, i heard PSN / PKG installed stuff will not work anymore. How hard is to the process to get them to work on the new cfw? Is there a way to overcome this?

3. What is this cex dex nonsense? Are they acronyms? Whats the difference?

4. Is there any reason not to upgrade?

Thanks.