When a lab carries out your test, they count the number of colony-forming units on the petri dish. They give you the results of the number of colony-forming units, for the number of grams or millilitres of test material that they put on the petri dish.
so 10^6 cfu/g means 10^6 colony forming units per gram of your sample. You would be able to see the colonies but might not be able to manually count each individual one because there are so many.
As for safety, it depends on what the product is but for cosmetics generally <500 cfu/ml or the equivalent in cfu/g is considered acceptable.
It is difficult to assess the maximum microbe growth in a formulation without a preservative because there are so many variables like the formulation itself (does it contain water or probiotics etc), the environments its in and any contamination that could have occurred.
My advice would be to NEVER skip the preservative!! There are thousands of preservatives out there that you can pick and choose from to suit your formulation and any claims you make.
Preservatives ensure consumer safety and increase the products shelf-life by helping inhibit the growth of microorganisms inadvertently introduced into the product during the manufacturing process or during consumer use. Without preservation, cosmetics containing water, would only last two weeks and microorganism contamination of yeast, mold, bacteria and fungus could cause skin irritation, allergic reactions, infections and more.