>>106982863
I use a 14" Lenovo laptop as my "main" laptop for actual work.
For documentation, notes (obsidian) and ssh sessions I use a Xiaomi Mi Pad 6 which is 10". It's a great size for when being more compact (and lightweight) matters. It's thin, small and light.

I always recommend to relatives to measure out the relevant sizes (7", 10", 14", whatever you're considering) and mark them on a piece of paper. I find just a screen diagonal to be too abstract, when you really see the size as a mockup you get a feel for what you do and don't need. 7" might be enough for example for a PDF if you either use it vertically or are willing to scroll more; if you want to be able to see larger circuits or maybe have one half of the screen for notes (obsidian) and the other for the PDF, then it's borderline too small. All depends on your usecase.

>>106982889
Not really in most purchases, it's like a 1-2% flat discounts usually. But if you seek out coin discounts and try to maximize them you can save a lot with them (though about half of those "savings" are fake as those listings are often overpriced to suggest larger coin discounts than they really offer).
Sadly the aliexpress app is just plain better than on the computer; search works, the different store pages like bundles etc are easier to navigate, most of the discounts etc. come from the app too. But it will schlurp your data in exchange for that.