If you are referring to setting up your country order strategies I can share what I do. Not sure if it's the best method, but it is what I have stuck to. I've looked in the forum myself and couldn't find a guide, with some conflicting information as well. So take what I use as a suggestion if you'd like. This is for quality.
There are two categories. Consumption by your population and spending by the government. You can find this on Financial Statement > Spending.
What I do, and many others as well. I set any product that is consumed by the population to 300q quality. The population buys those products at market price directly from your country. You are paid back for them, so even though you will be spending more on those products at 300q you will be paid back the same. Any quality above 300q that your population buys from you will still be paid back at only 300q. For example you buy eggs at 330q, pay 3.3x the market price for those eggs. Your population will buy them from you but only pay you 3x. You will lose the extra 0.3x.
The main reason for this is to contribute to the Consumption Quality Index, located on the Business page. This contributes towards your welfare index. Having those products at 300q will also allow you to if you choose, buy more in a surplus when prices are low. When in shortage and prices are higher you can sell them on the open market and will net more profits.
For spending by government. Anything under that section should be bought at 120q with the exception of weapons and ammunition. Anything higher than 120q, which is the minimum quality you can buy, will simply be wasted money. Your government will not consume higher quality products at a slower rate. Maintenance products and construction can become very expensive when you have a larger country. The difference between 1.2x and 3x can cost you tens to hundreds of billions extra per game month in a very large country. It is a hidden cost as well.
Not shown on the finance page but also extremely important. Make sure you set Elementary Schools, High Schools, Hospitals, Roads, Traintracks, Universities, Water treatment facilities at 120q. These are a one time permanent purchase, higher quality has no effect at all and will only be money wasted. For example roads are by far the most expensive infrastructure you will buy. If you order for example 54,807 miles of roads in one game month at 43.79m per mile. You will be paying 1.2 times to 3 times that price per mile. Buying those roads at 1.2x will cost you 2.88T SC$, buying those same roads at 3x will cost 7.2T SC$. A massive difference. This is also why is is important to check after purchasing roads/schools/hospitals check your trade page. If the quality is set to "Any" change it asap. It's a huge cost new players gloss over.
I need to test again, but I believe that buying lower quality ammo will be consumed at a higher rate than higher quality ammo. Not only that but for the most part having max quality ammo is recommended in most cases for a more effective military. I buy most of my ammo and weapons at 330q. For forts, airports, bases buy at 120q.
For quantity that's up to you more or less. I buy at 12 months low water mark with 24 months order quantity. This is so that I never ( in most cases ) have product shortages. Hopefully this somewhat helps answer your question.