Since it took Elspeth a day to recover, how long would it take the vampires of the guard? Half the time? Less? I've never seen a hard number for how much more mentally able a vampire is than a half-vampire.

In terms of raw processing power, vampires are about twice as fast/capacious as half-vampires. There are a couple of not-quite-qualitative differences (e.g. native architecture to handle seeing ultraviolet) that give them an extra boost beyond that in this sort of thing.

how is Chelsea at self-defense?

Chelsea's not a primary combatant by any stretch of the imagination, but she is very old and a key member of an organization that some people really don't like. She is better than the average vampire at combat.

There's no real range limit on the wolves' telepathy, right?

Right.

can we assume from this that Jake is still in contact with the pack?

Jake, as an alpha, has full unrestricted telepathy with any member of his own pack while both he and said member are in wolf form. He can also talk (only voluntary messages, no accidental letting slip of other thoughts) to his sisters when he and either of them are in wolf form.

Does Chelsea work on intra-pack membership bonds (i.e. could she make Jake's pack no longer his?)

Pack membership isn't the same sort of thing that Chelsea does. She could make Jake's wolves more willing to voluntarily change packs, but not force it without their agreement.