Canning your own recipes may not be safe due to acidity levels, density, etc. Also, some herbs in sauces may become bitter. It is always best to follow safe, tested recipes from reliable sources. The county extension office has them, USDA, various university websites, and the Ball company. I would recommend a Ball Blue Book. It is only about $5 and has many great recipes.
I am posting a safe recipe for some Italian tomato sauce for water bath canning.
If you follow the recipe exactly, you can water bath this one. If you change anything, you can put yourself at a risk of botulism. Otherwise, you must pressure can.

Italian Seasoned Tomato Sauce

10 pounds tomatoes
3 onions, finely chopped
4 cloves garlic, minced
3 tablespoons olive oil
1 tablespoon each basil, oregano, Italian seasoning
1 tablespoon salt
1 teaspoon crushed red pepper
1 teaspoon black pepper
1 teaspoon sugar
Bottled lemon juice or citric acid

Prepare Ball brand or Kerr brand jars and closures according to instructions found in Canning Basics.

Wash tomatoes; drain. Peel, core and cut into small pieces; set aside. Sauté onions and garlic in olive oil in a large saucepot. Add tomatoes and seasonings. Simmer about 2 hours, stirring occasionally. Press mixture through a sieve or food mill; discard seeds. Cook pulp in a large, uncovered saucepot over medium-high heat until sauce thickens, stirring to prevent sticking. Add 1 tablespoon bottled lemon juice or 1/4 teaspoon citric acid to each pint jar. Carefully ladle hot sauce into hot jars, leaving 1/4-inch headspace. Wipe jar rim clean. Place lid on jar with sealing compound next to glass. Screw band down evenly and firmly just until a point of resistance is met - fingertip tight.

Process 35 minutes in a boiling-water canner.
Yield: about 4 pints.

For altitude adjustment increase processing as indicated below:
1,001 – 3,000 ft………...5 minutes
3,001 – 6,000 ft……….10 minutes
6,001 – 8,000 ft……….15 minutes
8,001 – 10,000 ft……...20 minutes

As for onions, there are many recipes that contain onions for canning. No problem as long as you the recipes, method, and times are followed.

When combining various sizes of jars in canning, can for the largest size jar. If a recipe has the same for both pints and half pints, then follow that. Otherwise, use the time for the largest jars. If they are 12 oz., use the time for canning pints. The 4 oz. are the same time as half pints. With combining pints and quarts, use the time for quarts.