I've had to get my book out on the cheese one! It's a max of 110g of cheese a day, and 3 tablespoons of cream (double, whipping, sour). I stuck to those limits for induction and then forgot all about them.

It never affected my loss rate though.
I'm thinking you could substitute the salmon for something like ham? I'm not always good at knowing what should go with what, I just throw it what I have/fancy.
Ok so back to your other questions:
Sauces - not sure on all of them as I'm easily pleased and just threw mayo and low-carb ketchup on everything! Anything with minimum/no sugar and no flour ought to be ok? You can make your own salad dressings (I did once and too lazy to bother after that).
My snacks were usually Babybels, straws & cream (after induction) or fake choccy mousse, in maintenance I ate an awful lot of dark chocolate but I felt I'd earnt it.

Oh and nuts once you reach that phase. You do honestly feel the need to snack much less though, after induction my never ending hunger was gone which I didn't think possible! It comes back a bit in maintenance but you have to find your own balance at that point.
Choccy mousse is just 3 tablespoons of cream (whipping or double), 1 teaspoon of cocoa powder and 1/4 teaspoon of Splenda all whipped up for a minute-ish. You can adjust it to your taste though. It's gorgeous with raspberries which you get to have as one of the first phases I think.
If you don't want 3 meals a day then don't, more regular smaller ones are fine, it's the carb count that matters (and for me getting enough carbs was the struggle in induction!).
Have a read of these forums for more meal/snack ideas or grab that cookbook - there's loads of good ones. https://www.pig2twig.co.uk/forums/
The sparkling water's fine I think, I drank plenty of it anyway.
I know how you feel, I was a total carb addict and never thought I could give up my bread and potatoes! Never felt the same about bread since Atkins though. Also I was rubbish and snacked on boring stuff like cooked bacon etc. as I had no idea what to make but reading some forums was a Godsend as everything you can think of has a low-carb substitute from people with more imagination than me!
When you're further along you can buy low-carb products like pasta, sweets and wraps, etc. which might help? Very pricey though.

Keep saying to yourself 'induction is only 2 weeks!'
Hope that helped a bit!
x