Some DEX questions

[Himeko]

Hi,

Forgive me if this is already answered elsewhere. I've been looking here and googling for the past 2 hours and came out even more confused, there is a lot of mixed information, old posts, contradicting info etc.. so a few straight questions please.

I am running CFW 3.55 with Multiman 04.07.00 on a fat PS3 with hardware ps2 etc, it's one of the first few sold during the Tokyo launch, in fact it even says "Made in Japan" on the back, it's one of the first batch not made in China in the initial launch back in 2006.

1) To convert to DEX+higher FW, is it like.. I convert to DEX, then I upgrade to official 4.21 FW, and the DEX status remains?
2) ^ assuming 1 is right, do we need some special kind of official 4.21, like, a debug version of the FW and not the official one?
3) ^ if 2 is the case, (need special debug fw), would installing OFW remove DEX status?
4) Once on DEX, can we downgrade to 3.55, and then proceed to reinstall the common 3.55 CFW again?
5) Will all the backups that worked with 3.55 cfw+mm still work? I guess through the new mm, but:
6) ^ will they work from INTERNAL hard disk? I've seen very mixed/confusing posts about this, with people saying only external HD works. I got a 750GB internal disk with all my games, resorting to external is just ugly/messy.
7) I guess PS2 backups are out of the question.. but can you play PS2 ORIGINALS from locked regions through DEX? My PS3 is japanese, so currently my US/EU PS2 originals don't work (consider my PS3 has HARDWARE emulation, not software as is the case from later models post 2007).
8) Does homebrew work, besides mm? (most hb sucks anyway though, not that worried about that).

That's mostly it. I had doubts also about 3.60+ games but that seems even a lot more shady at the moment with all kind of confusing info about it, so nvm that part.

[Shaitan]

When you convert to DEX you can up&downgrade between eg. 4.21 and 3.55, you won't ever "accidently" lose DEX status, you need to flash the CEX flash backup in Multimannto convert back to CEX/retail. DEX firmwares are a different set of firmwares altogether but 3.55 DEX CFW/MFW is basically the same as Kmeaw so all your old backups and homebrew will work, only certain homebrew will work on 4.21. Internal/External compatibility for regular backups is the same as normal CFW, BUT all backups you want to run on DEX BD-EMU on higher firmwares like 4.21 can only be installed on External or via LAN connection to your computer.
Sorry I'm not sure about ps2 compatibility, maybe someone else can answer