Footer size and spacing depends entirely on the load they need to support and the dimension of the beam and how it needs to be supported. The greater the spacing or the greater the live load (people on the deck) the larger the footings need to be. Be smart and take the time to find load tables and footing specs and how to determine the static and live load from the deck. This is not something to Mickey Mouse or do on the fly.
Consider going up a dimension as you do not really know what you are doing. If the plan calls for 2x8 joists then go to 2x10. If it calls for posts every 7 feet then space them at 6 feet. If footings are to be 8 inches deep then go with 10 or more inches.
When a deck is at ground level you can wing it and many deck contractors do so. But with a deck off the ground it becomes more complicated if you want a SAFE deck for you and your family and friends.
Consider going up a dimension as you do not really know what you are doing. If the plan calls for 2x8 joists then go to 2x10. If it calls for posts every 7 feet then space them at 6 feet. If footings are to be 8 inches deep then go with 10 or more inches.
When a deck is at ground level you can wing it and many deck contractors do so. But with a deck off the ground it becomes more complicated if you want a SAFE deck for you and your family and friends.