Type 1 Basic Questions About Timing And Measuring Sugar

To be honest, if you want to be 100% accurate, the answer is "it depends".
The usual advice is to take insulin 15 - 20 minutes before eating. However, whilst insulin is absorbed at a (reasonably) constant speed, the carbs we eat are ingested at different rates. For example, pure sugar will affect Bg quickly (which is why we eat it when we hypo) whereas something with fat in it (pizza, chocolate, ...) will be slowed down by the fat.
People using Libre or CGM are able to work out when to take their insulin depending on the foods they take in order to keep a flat profile.

To my understanding, the advice to test after eating is for someone with type 2 to understand if the impact the food has had on their BG and whether they should avoid it or not.
I have never been given this advice as someone with type 1.
I test
- any time I wake in the night
- before every meal
- before driving
- before and after exercise
- if I feel "off"

As for cleaning your hands with alcohol-based cleaning products, I have read somewhere that these may contain something which can affect your BG. It is better to clean with good old soap and water if you access to some.
But bear in mind, there is a lot of approximation going on with testing, carb counting and insulin dosing: meters are usually accurate within +/-15%, carbs vary, insulin doses are intelligent guesswork.