A couple mechanics questions (BRDs/general.)

[Felessan]

How are DoTs calculated? Is it static, or dynamic?

Static, i.e. you should apply you buffs before dots going out.

If dots are static, do they roll?

Afaik no, they reapplied with new stats.

How many cooldowns can be squeezed into a GCD? I've heard both 2, and 1, but using 2 seems to be pushing it with the animation lock on some of them (like internal release.)

You have around 1 sec "mandatory" global cooldown even after offcooldown abilities, so you can sqeeze 2 abilities into a GCD, but next ability will be pushed a bit (you'll be uanble to use it just when GCD ends).

What takes priority to fill a GCD? Bloodletter proc, or popping a DPS cooldown?

Depends on situation. Normally it's bloodletter and misery end, but if you need to reapply dots soon and have more than one cooldown it's better to pop up cooldown manually as you want to stack buffs for dots.

What damage type are venomous bite/windbite counted as? Are they buffed by foe req, or DRGN piercing debuff, or nothing at all?

Piercing as all other damage from bard.

does ballad restore enough MP to keep 100% uptime on it like it does when you first get it?

Nope, you'll be able to keep it up for around 1 min.