@Sewot Once I graduate to oaktag for blocks, I will probably buy a notcher, simply because it's a cleaner way to work. For now I snip with scissors.
Once I'm happy with a pattern, I include all seam allowances and hems; simply because that is the most time efficient way for me to work for me.
As a home sewist, there's no "sewing police" involved. While notching patterns with scissors may take an extra minute or two, adding seams allowances each time I cut a garment would probably take an extra half hour. A professional tailor must be aware of every moment of time he wastes, as each wasted moment decreases his income. This is why there are so many established rules to the crafts of pattern making and tailoring.
If I buy a notcher, the truth is that I will probably never use it enough to recoup the cost in time savings even if I calculate my time based on a minimum wage. But - the neatness of my work product will make me happy.
Much of what you do for you will just be personal preference.
Take the practice of tailoring the front edge of a jacket lapel. Typically a cotton twill tape (1/4"-3/8") is hand-stitched in place to stabilize the front edge and reinforce it. This tape has been manufactured for this specific purpose and others for decades. Yet it is also an accepted practice to carefully trim the selvedge edge of a shirting fabric or even an old sheet to use for the same purpose. Is this the most time efficient manner? No, but it's the most frugal. And it's a time effective substitute if you've run out of tape - or your supplier didn't receive his shipment. Would your customer want to know the front edge of his $3500 sport coat was reinforced with the recycled edge of your grandmother's muslin sheets? Of course not, but he'll never know. I, on the other hand, would have a sweet moment each time I consciously looked at that jacket lapel. And I know my grandma would approve.
I buy sewing aides when I know they will make my work easier or if I believe they will give me pleasure to use - when I can afford them.
The only item I wish I had bought decades earlier is a REALLY good pair of shears. What a HUGE difference they make. Also, thread snips are wonderful inexpensive gadgets. Especially nice for my slightly arthritic hands.
Buy what you need as you determine you need it. Too much stuff can be more restrictive than not enough. Some people need something called IDT on a sewing machine. I'm not even sure what it is. Some newer sewing machines always stop with the needle up. I think the two concepts are related, but I know this for a fact: I need to ALWAYS be in charge of how my needle stops at the end of a seam manually. Even if they developed a machine that read the operators mind for instructions on how/where to stop the needle at the end of a seam - I wouldn't NEED that either -as my hand is capable of stopping the hand wheel where needed - while my mind is thinking, "Wow! Brad Pitt sure was pretty" as I glance at "Thelma and Louise" on Netflix.