^^ what he said. You may be better off with a used
laptop. then you can always get a new battery from Amazon and get good runtime. standard screen sizes are normally between 13 and 15 inches. smaller then that any they are going to be hard to see all of the tables. great for potability. also will tend to use non standard keyboards. above 15" gives a lot more room for display content and a full sized keyboard. often has a slot for a second hard drive or DVD drive, etc. Mine is a 17" and does fine for tuning in the vehicle but I'll admit it is a little larger then optimal. but love the screen real estate and number pad. good battery life at 4 hours bit some of the little ones are pushing 8+ hours now.
the newer compact or netbook or what have you are now using the M.2 and NVMe type hard drives which are somewhat like using a thumb drive as a hard drive but internally. good for getting bumped around because there is no moving discs and sliding arms like the traditional types. so if you are getting a somewhat newer one you can see if it contains one of these. the operating system can take up to 10 gb or more and saved files and software can quickly eat up space so I'd shoot for a minimum of 100 gb of storage but you can realistically get away with 40 gb or so if you where mindful of getting rid of junk files and other unessential programs
For CPUs, EFI live can run on much older hardware. an old Celeron processor could do it. but I'd stick with at least an intel i3 or or equivalent as it still has to run windows and boot fast enough to make it worth using. if you are planning on keeping it off the internet for most of its life and really only using it to update EFI live or email tune files, etc then older generation windows such as XP or 7 is preferred over 8 and 10. but no new laptop can be found with anything less then 8, maybe even 10 now. some are even being shipped with 11 on them. I'd shoot for finding one with windows 7 if you can
Toshiba, HP, Dell & Lenovo all make good laptops. I really like the Dell Latitude for their simple straight forward work design. made for business so not a lot of bells and whistles or other flashy stuff. just a simple workhorse. I have an HP now but if I was to do it again I'd probably go with a latitude.