You almost always want CTR and ASI UVs, not damage UVs. A damage UV applies to one monster family only, while CTR and ASI UVs apply to all monster families, Vanaduke (who is not in any family), and opponents in Lockdown. This isn't to say that damage bonuses aren't valuable; you just want to get blanket damage bonuses from armor such as Shadowsun and Skolver, Barbarous Thorn Shield, and trinkets. (When the game launched, there weren't so many ways to get blanket damage bonuses, so damage UVs were more valuable than they are now.)

Whether you want CTR or ASI depends on what you can get from your armor and shields, what weapons you use, and what your play style is. For example, if you plan on wearing a lot of sworder armor, then you'll be wearing Vog Cub a lot, which means that big ASI UVs on your sword may be wasted; maybe you'd rather have CTR UVs. On the other hand, you probably want ASI on a Gran Faust, because the charge is so slow that you may not use it often. DVS and Argent Peacemaker also have not-very-useful charges, so ASI is preferable on those.

Shivermist Buster does a little damage, but not much; its point is to spread freeze everywhere. There is no question that you'd rather have CTR than damage bonus on that thing.

there is no leg armor. and shield defenses and armor defenses are separate.
anyways, if you mix different damage defenses in a sinlge set like, for example, radiant silvermail (piercing and shadow) and vog cub coat(elemental and normal), say eachone gives 10 bars of protection for each damage .youll get 5 bars of each ( so yeah, theres reduction).

i have a dragon scale helm with a fire high variant, but heres how stuff happens to me (btw, im using a volcanic plate mail, that also has fire res.) : T1- no fire; T2- rare and small duration Fire from monster attacks, no fire from grates. t3 Stratum 5- rare and small duration Fire from monster attacks and none from grates, stratum 6- no fire from wisps, fire from grates (always, but not long duration) and monster attacks (fairly rare, short duration).
there is quite a difference between fire resistance and fire resistance with a max uv, believe me.

Generally people prefer to have shadow and elemental defence, since these are considered to be the harder enemies to block (slimes and beasts generally being a bit slower and easier to dodge with their attack telegraphs).

Shock is usually considered the most dangerous status as it interrupts attacks, charges and shielding with its spasms, as well as dealing elemental damage. Stun reduces speed and is good in t3 LD games, but only occasionally in PvE. Freeze is debatable; it roots you in place, but doesn't actively deal damage and can be broken by a friend, so it won't trouble you unless you're beset by multiple enemies or on your own. Fire deals pure damage without interfering in movement. Curse is rare, and not much of an issue if you're with teammates/have extra weapon slots since you can shield whilst they fight/still use a different weapon. Poison doesn't actively do any damage, although it can be lethal when paired up with lots of other sources of damage - say, fire status in C42, or if you're being mobbed by enemies.

A Vog Cub piece with Fire Max! would be excellent, since a single Vog piece on its own isn't enough to grant immunity to fire. For that matter, neither would two pieces of non-UV'd Vog (double Fire Max!), or, at least, it wouldn't grant immunity to all types of fire. Triple Max! will provide you with enough resistance to make you immune to most causes of fire, however.

Most people prefer to mix and match armours according to the situations they might encounter - say, a Skolver set for a sword-user in Lichenous Lairs, and a Vog Cub set for an FSC run, or full Shadowsun for a gunner in UGWW and PMoS/Shadowsun for FSC.

One popular all-purpose outfit for sword-users is Divine Veil/Skolver Coat, which gives a decent amount of each defence, coupled with a single Max! of Freeze, Shock, Fire and Curse along with a sword damage bonus Med and a fiend damage bonus Med to boot. (You can use the Skolver Cap/Divine Mantle, but a) you wouldn't get the Fiend bonus and b) it looks pretty weird.) It's not the best setup, but it performs adequately in most situations other than Danger Missions and Shadow Lairs. It's reasonably cheap and easy to obtain since all recipes may be found in HoH. The gunner's alternative uses the Justifier Jacket; this isn't quite as good as the sword option since it gives an ASI Med bonus to guns and has Stun resist as opposed to Freeze, but it is still a pretty decent all-round setup.

(If you're bombing, too bad because all bombing armour is normal/elemental and your only options for getting some of all defences are Radiant Silvermail, which is pretty pants in most cases, or losing out on offensive bonuses.)

It isn't possible to get two of the same UV type on one piece of equipment. Say I had a Valiance with ASI Med; I could not then roll a double-UV ticket on it in hopes of getting another ASI UV. That doesn't prevent you from rolling shadow defence on an armour that already had shadow defence, however. In addition, despite what the tooltips say, it is possible to go beyond the edge of the armour defence indicator - the Plate series, for example, seem to have maximum defensive power against Normal damage, but if you rolled a Normal-damage UV, it would still have an effect on the protection the armour gave. (Perhaps not much of a noticeable effect, but it would still be there.)