1) I don't know a "good" one. lot of guides are telling users different things. some are short, some are longer to follow.
You may have :
1-
https://sites.google.com/site/completesg/
But you need to change one thing that they are telling you. they are still telling users to install a bad cIOS version. If you follow this guide, don't install d2x r53, but r52 instead. (all r52, or on Wii all v8 final, don't mix versions)
Edit : not needed anymore, someone fixed the guide and properly tell users to install r52 in both slot ! at last
2-
http://www.wiihacks.com/showthread.php?t=96886
this one is more complete with things like Priiloader covered, and more "step by step". Though, it uses old tools, and make you follow quite strange path to achieve something easily done another way.
3- You can also use modmii program which will download all needed files and tools, and will generate a custom guide based on your own replies. that's probably the easiest and more complete one in less steps.
4- short path : if you are on Wii 4.3 (not vWii), install
HBC and bootmii following
Hackmii.please, then install
cIOS d2x v8 final base57 in slot 249. Done. that's all you need to make everything compatible. (HBC + 1 patched IOS, that's all !)
additional steps are for security (priiloader, in case you plan to do stupid things to your console's file system), or outdated/deprecated mod (Hermes cIOS, cIOS 236, patching sysmenu IOS, downgrading sysmenu, etc.), or updating outdated IOS (optional)
2) Yes, as long as you use FAT32 partition !
do not follow any guide telling you to format your drive to WBFS, it's an old and deprecated format, and therefore an old and outdated guide to follow.
MBR is better than GPT for compatibility (old homebrew can only read from MBR partition table type), Primary partition are better than logical, 32k/cluster is also better for compatibility.
so, MBR primary FAT32 32k/cluster, 512 bytes/sector if possible ! (that's a hardware value, you can't change it. but homebrew who care about sector size should now be compatible with all other sector sizes, so it's fine)
3) Some flash may work in read mode, but freeze in write mode (no disc dumping possible). Some Flash may not work at all.
Prefer using a Hard Disk. USB2.0 have better compatibility, as newer disk drive seems to require new initialization process that current cIOS don't have. But if you have a USB3.0, there is a workaround, so it's fine too.
4) I can't answer that question. Sorry.