Ok to clear some things up...
1. Base dmg doesn't do ***to magical ws. Instead it uses lvl+2 where weapon dmg would be. So martial knife is just as good.
2. magical ws don't use fstr. They use fint where fstr normally would be or some dstat factor with a multiple that is calculated after ftp. Supposedly some ws might have neither but I've yet to see testing that was conclusive. Obvious exceptions are of course spirits within and atonement
3. Kinda already answered but you can't double/triple/quad whatever attack on magical ws.
4. Already said but dex/int worthless. MAB does help but it's the last thing you should add as brew gives +900 MAB severely devaluing it.
5. For gear if it's wind day get obi for that if not elemental belt if not something mab. tp bonus knife. ws gorget. After that only mab will help you in other slots
6. Atmas should use gales, 1 of the +50 MAB ones and tp bonus one. The question about griffin claw is a no. It specifically says when 2hd weapon is equipped.
7. Unfortunately dnc doesn't get that good of native elemental ws and as far as I can tell earth crusher is the best you can get from a subjob is earth crusher which is barely better.... However if you can get an extra 20 more skill pasted the lvl 90 cap on dnc for swd (ie merits and suppa) and chose the right subjob you can get sanguine blade.... which given best setups of both would do almost 50% more dmg.
8. If you can and do sanguine blade similar idea except tp bonus doesn't mean crap not sure if you can get a MAB weapon other than trial dagger... but if you can. ws gorget/belt or dark obi. mab in other slots making sure to still have 300 skill. Atmas use cosmos, banisher and one of the 50mab ones.
8. If anyone is wondering why I call the other elemental ws bad and SB good it's mainly because SB uses dint while the others use fint... dint caps 1276 after the 2 multiplier but is added to the rest after ftp. fint caps at 32 but is added before ftp so even with a ftp of 4.0 only ends up adding 128 vs the 1276 good magical ws.