OK, let's leave the food decay and sandfill things and volcanic eruptions for now. The first is an overstated problem: Just get your food in a stockpile, preferably underground (I'm thinking more for protection from animals than spoilage) as soon as possible. The second two are really weird, should not be happening, and make me think you might have a buggy installation.
There's two basic schools of thought with regard to where fortresses should be started
1, somewhere with magma
2, On sedimentary rock (the stuff that shows in white letters on the embark screen) plus trees.
For both, a brook is a help as well. But don't embark on an aquifer (blue lines in the soil layers), or on anywhere there's no soil.
If the biome is freezing, don't go for a brook, go for an aquifer instead. It's the only way to get water and it's relatively easy to penetrate an aquifer in freezing conditions.
As to the schools of thought above, 1; (the magma route) will give you smelting and forging once the infrastructure is in place without need for fuel. The disadvantage is the fire imps can pose a notably early-game threat and areas with magma are often very poor on useful metals. Sometimes you get lucky and have lots of iron, sometimes you break even and get copper, and sometimes you don't get anything beyond a few aluminium pockets.
2; (the sedimentary forest route) will give you iron in abundance but you'll have to burn fuel to smelt and forge it. This is not as bad as it sounds because sedimentary rock contains butinimous coal and lignite. A couple of veins of the former will probably provide a fortress with all the fuel it needs for years and by the time it runs out you'll have enough ironmongery to hold off the golden horde. Note that you'll need to burn some wood to start with before you can start making the coke.
Of the two options, I think that option 2 is stronger and more dependable. Option 1 appears to be more popular. This seems to be because many who play this game started playing at a time when magma was a guaranteed feature of every fortress and they can't imagine going without it. If you have some coal seams, the magma will only be really missed if you want to melt down a lot of captured equipment (just sell it. If you're on sedimentary you won't need the bonus iron).
Starting without either magma or sedimentary will make for a challenge. Starting with both can be done in some areas but it's a struggle. SOmething like one in every ten worlds might have such an area.
I haven't mentioned steelmaking, because it's a tedious process requiring flux and coal. If you're on magma you probably won't even get to try. Even on sedimentary, the process is so irritating and fuel-intensive I gave it up a long time ago. Note that though steel is the strongest common metal, it's also got a really high base value, meaning producing it will attract goblins in heavy numbers.
Digging into a mountainside is a traditional way of starting a fort. I like to start on the flat and dig straight down, as a flat area is much easier to fortify than a bunch of slopes and I tend to play with lots of local opposition.
Don't embark anywhere without trees unless you really want a struggle. Carrying wood with you is possible, but the time it take to haul useful quantities of wood inside can put a real crimp on the first season. Getting wood from trading is also quite hit and miss.
I recommend taking lots of copper picks, even at the cost of an axe. Set everyone bar one woodcutter to work mining right anyway. It doesn't matter what their "real" jobs are. They can start doing them when you've made a place to live.
As for biomes. Haven't really seen too much different between the various savagery levels to be honest. "Untamed/Joyous wilds" might have one big predator over the calm/serene areas. Sometimes not even that. The evil biomes are a very mixed bag. It would be more useful to know if such an area has undead or monsters rather than it's savagery level, but there's no way of telling (some people will tell you that the difference is colour-coded in the embark screen. This seems to be wrong). Undead areas are more fun but generally more dangerous, though terrifying monsterous swamps have an evil reputation.