@Lost_Lombax Hello, welcome on forum and thanks for the opinion. ^^
About ERK dumping, I don't remember now but if key appears, then it is probably valid (48 bytes long). But would be wise to test it anyway to be 100% sure.
Activation (act.dat) and licenses (*.rif/*.edat/*.mln) are inside exdata folder. But they will work only on this specific mother board. In other words, they will not work on different console. That's why You should convert (decrypting by IDPS and extracting klicense from it) *.rif's to *.raf (i.e by Apollo). Activation will work after changing HDD (the same with *.rif's) but on another PS3, You will need to make activation by ReActPsn, or better now, by Apollo SaveData Tool, or just by official way.
Problem with FTP Servers is they are not stable. If You experience transfer freezing, You must re-transfer all files on which it froze (FTP Client logs each connection) because they will stay broken.
You can read data on Windows via:
https://www.psx-place.com/resources/ps3-hdd-reader.1278/
But do not afraid of Linux (it is now just better Windows

). If You don't want install it, You don't need to because most distributions works from RAM. Just put on USB by e.g Rufus e.g Mint with Cinnamon and boot PC from that USB.
https://www.psx-place.com/resources/ps3-hdd-decryption-helper.1293/
But with writing to PS3 HDD, there is some real struggle.
You don't have choice but to format new HDD for the reason that Windows cannot made PS3PT partition tables, in case of NOR models, recreated VFLASH partition, not support UFS2 filesystem, and on top of that, cannot encrypt it in a way user choosing.
In theory You cannot use at once two HDDs because once one is assigned, another replacing it and old become unrecognized until change in xRegistry been made or of course until format be performed. However, reports are mixed, some people says that they can freely using few HDDs (of course all formatted on the same PS3 due to unique encryption key(s)). But normally You cannot do that and no one knows why it is possible for some others (models doesn't matter as reports mixed for NANDs and NORs).
If something goes wrong with restoration, You will be able read anything on PC while You have ERK and ATA/VFLASH keys which came from ERK. However, Windows is aggressive and misleading, so remember to
NOT agree for disk initializing if You don't want become my client for data retrieving.
NEVER again install OFW. Once You have installed CFW, You don't need OFW for anything. When You put new drive, feed console on USB the CFW, not OFW/HFW.