yes 28-30 gram total output (actual volume is not that critical but consistency is important when starting out) weighing the output as you pull helps narrowing down the number of variable you have to adjust!

I'd really stick to doubles at first, the 'norm' (Italian old school that is) is to use 14 g for a double and 7 g for a single. depending on what filter basket you are using you may be making things more difficult if it os overloaded.

If the roasters you get your beans from sell within a week from roasting and you ask for a 'starter cofee'I'm sure you should be OK.

In Italy we do 7-14 (single-double) and tweak around that but pretty much the variation is minimal, if you go in NA, Australia etc, to put it simple where they are used to bigger cups of coffee basically, lots of milk stuff, there is a tendency to dose higher. So when you read amounts take into account different habits.

If you take the basket as integral part of the process, which in fact is, you can see how having a basket designed to have a certain flow with a certain amount of coffee and filling it with a different amount will start to throw some things off.
Somewhere your machine will have written what is the average amount of coffee the basket should hold, but if you have a basket that intends to be used with 12-14 grams trying to fill it with 18 grams would be a problem. If one wants to over-dose the best thing is to get a basket meant to hold the quantity they want to use, which isnt just a taller basket if its properly designed. (and depending on the machine it might not always be possible to go too high, take small boilers for example: you will start encounter temperature stability problems during the shot if you have to pass too high a quantity of water to satisfy the amount of grinds)

Also, often the process suggested is to overfill the basket then push off the extra and tamp and brew. Depending on your basket, beans etc that could give you more grinds than optimal, or a somewhat different amount everytime. If you have a scale do yourself a favor and weight the coffee you will be filling the basket with, you can weight directly the beans if you know what you end with once they pass out the grinder. It doesnt matter if you are a bit below the rim of the basket. You will reduce your waste and be more consistent (and for the same reason quantity marks in the basket arent that reliable).

Its not that this or that methods are necessarily wrong or that one cant finagle a decent cup of coffee through different routines but, at the beginning, going with the easiest methods is worth it. And its important to be consistent or you will be running in circles if there are lot of variables.
Once you learned you can start tweaking whatever you like (which includes freezing beans, dealing with fresher and older beans and so on, just use beans that are all close to the same age at first).

PS: that gauge on the machine might tell you if something is off at extremes but you would see that in the cup anyways so dont take its indication as the bible.