Partials and Fulls after Multiple Simultaneous Queries

Agents will assume that you're querying widely and that other agents are reading the MS. Only let other agents know if you get an offer of representation. When you have The Call with the offering agent, you'll work out how long you're going to wait until you respond yes or no—usually 1-2 weeks. Then you inform the other agents (who requested material) of this time frame to give the a chance to read and offer or decline.

Nah, that's standard practice. In fact, a great agent will encourage you to follow up with those other agents and make sure you're making the final choice you feel best about.

No, only contact agents if you get and accept an offer, anything else is not their business.

It's normal and expected that an agent will ask for a full, expecting that other agents may have the full. On rare occasions, if an agent is feeling pretty strongly about it, they might actually ask for an exclusive on the full, which just means--if you AGREE to it, that is--that you stop querying, but you're under no obligation to pull back fulls that other agents may already have.

In the event that you get an offer, it's like Sparverius says, it's not a big issue. Most agents, if you notify them that you've gotten an offer, and then give them your one or two week deadline--I gave my potentials two at the time, because it was summer, but one is pretty normal--will usually thank you for notifying them about the offer, and then backlog everything else to give your book a priority reading to see if they want to counter-offer.

I know it's tough to see, but if you're in this position, YOU'RE the one that's actually at advantage here. So don't get too caught up in inconveniencing agents with short timelines on the read. A lot of the time, they'll go through it and figure out pretty quickly that maybe your book wasn't for them after all, but some of them may make counter-offers, and if that happens, ball's in your court.