Maglite has some great X50v (I actually read the post and read it was x50v, not x51v) ROMS.
You basically have two ROMs to choose from: Maglite or LennySh.
Answers:
1. Maglite wants you to update to A02 because A02 uses a different bootloader than A01. Therefore after you flash to A02, the bootloader will recongnize the WM6. So you need to flash to A02 to upgrade to any kind of WM6 ROM.
2. No, LennySh has also released his A09 version of X50v's ROM. Personally and IMHO, I think LennySh has the best ROM for any Axim device. His L11 (Successor to A09) is being beta tested. Whether you want to wait is up to you.
LennySh A09-
Dell Axim x50v WM6.1 A09 (LennySh Edition) - HTCGeeks Forum
3. I read his post. If he says up to 8GB, I suspect (I do not know for sure) that is ONLY supports up to 8GB, NOT 16GB.
Recap about your problem here:
You have MagLite's A01 ROM. He wants you to upgrade to the OFFICIAL A02 ROM before flashing his WM6 ROM. Since your Activesync is unreliable, I suggest using the bootloader method (Wireless+power with reset button). But I know Dell does not give you a nb0 file for their OFFICIAL A02 ROM, you have to use their installer.
So my suggestion is: I am downloading the official A02 ROM right now. I'll see if I can extract/get a .nbo file from that. That will allow you to install via bootloader.
So Please Wait