Increasing my pancake recipe..Are soda and salt in a different ratio than the other ingredients?

In a pancake recipe, it is unlikely to be a practical concern.

The reason these ideas get started is because:

1. Small recipes have intentional rounding-off errors to make measurements simple (1/2 tsp for example, instead of .4321 teaspoons)
2. Scaling up may magnify error
3. In yeast raised doughs, where yeast grows exponentially over time, scaling yeast up linearly can have some complex feedbacks with proofing times and temperatures given how long it takes to work on a larger volume of dough. Because salt interacts with the yeast, it is also a crucial ingredient for scaling. That doesn't apply here.

Pancakes, in particular are very forgiving and flexible. They should scale linearly, in practice.

If you are exceptionally concerned, you can find a commercial recipe (often called a formula) which is expressed by weight and is much more accurate. These should scale quite effectively.

One issue you may have is how long it takes to cook the larger batch of pancakes, and that you will be losing leavening from the batter during that time. Unless you have four people working four griddles, you may be better off just making a large batch of dry pancake mix (everything except, typically, fat, eggs, water, and dairy depending). You can then mix in the liquids in smaller amounts as you go along, essentially continually creating fresh batter for yourself.