Your biggest problem is that you are trying to make a fort in a terrifying biome like you would normaly make your fort, though the strategy is 100% different.
It has to do with blocking your self off from the surface and living underground off farming until you hit the caverns.
I've been building an above ground fort in an evil/neutral biome for quite some time now, and it's radically different from the standard 100% evil embark.
First off, don't bring armor. It's far too expensive on embark, and the best it's going to do is turn a scratch into broken bones, because the undead are all grotesquely powerful. If your Dwarves end up getting hit by the undead, you can bet they're not going to last long for several reasons:
- RNG spiting you.
- Happiness drop amongst the initial seven is devastating.
- Getting knocked over for a Dwarf is a death sentence.
Skip the silver warhammers. If you
must embark with weapons, take wooden crossbows or copper warhammers. Copper warhammers are incredibly cheap, and incredibly effective.
If you're certain you can hold off the undead for the first few days, skip the weapons and instead bring the materials needed to make those weapons, which saves a helluva lot of embark points. This is pretty much required if you're going to pick crossbows over hammers - but I can say this, my normal embark with 3 proficient hammerDwarves was torn down very quickly by undead Dingos, and my above ground embark with 2 marksdwarves has lasted me to this day.
Marksdwarves are brilliant against the undead by the way. Build your fort (or dig?) it in the safe side, keep an armed marksdwarf or two on guard and you're set. You can even safely secure sections of woods to clear, and once your military is big enough - you can even actively kill undead roaming your map with showers of wonderful zombie bone bolts. Just make sure your butcheries are in the neutral side.