SARADA,
I figure about 2 - 2.5oz As Purchased salmon per person depending on what else is on the menu and on the clients. We used to use atlantic salmon in the 8-10lb range, but you are realy only limited by the size of your equipment. We used these big "army" roasting pans to cook 2 salmon (a little snug) each in. These pans are very expensive though (>$300) so don't rush out to get buy one just for this.
If you are using hotel pans you will need at least a full 600 pan to due a deep poach, you can also use a full 200 for braising. If you are going the deep poach method invest in some cheese cloth, so you can hammock the salmon in and out. With hotel pans you will also need to buy smaller fish.
One of the big factors I have found with serving these salmon, is that they start to look bad after being 1/2 picked over (we served ours as self serve, and the tongs really tore up the fish). This is another reason buy smaller fish, so you can keepem fresh looking. I think a 4-6lb salmon is good size to go with (especially if its part of seafood/rawbar). This also depends on the serving area. If the table is huge, that little fish is going to look lost.
Without knowing about your clients, 3ea 4-6lb salmon should be enough with some comfort room. There are many factors involved that only you can assess.
Aromatics, you've got a good mix there. Its really a matter of personal taste. I like water, white wine, white wine vinegar, mirepoix(celery, onion, parsnip/carrot, fennel greens/bulb if you like), bay leaf (fresh is better), peppercorn, pickle spice, dill, lemons. (put your spices in a sachet to keep things neat). The list goes on depending on theme and clients. (If your clients like old bay seasoning, throw a little cardoman in the mix). When you're looking this stuff up the french guys call it
court boullion.
As far a technique goes, IIRC this
book had a pretty good step by step illustrated method.
Another note on equipment, if you don't have access to a sharp deli slicer, you'll need a madoline or v-slicer. If you are going to glaze the salmon with aspic, you'll need a cooling rack. If you've got a fish spatula for serving, bring that too, cause tongs tear the fish up.
Man this was a job ago, and I've got salmon on my mind!
I do like your signature salmon dish, I think I'll run it past the gf.
As for contracts, these are you first and last defense. You can add a clause that adds a per capita price if extra clients show up. You should also have a clause that provides for a minimum guest count (i.e. you book a party with a 100 min, only 50 show, but you bill for 100). Contracts that spec how many pieces or oz are especially good at events that you have little control over. In general, running out of food is a very bad thing. You probally know most of this though. Shroomgirl is a good person to talk catering contracts with.
Another tool that is very usefull is the end of event "survey." Its a one page thing you give to the host (before requesting final payment) to evaulate the service, food, etc. In addition to giving you valuable feedback, its an additional cya if they try to dispute the bill.
Always, always get a 50% deposit. (You know this I'm sure, but its so important I'm having it put on my tombstone) You also might want to get the ability to process credit cards.
Hope I didn't put you to sleep. Good luck with your event.