I use my laptop mainly for trading and Microsoft Office apps. I only use one external monitor. Is an i5 processor and MX250 graphics sufficient?
Probably yes... so long as your trading apps are "routine". (Routine/canned apps load into RAM and run from there by design. If you work "custom applications", they may require more CPU horsepower and RAM.) In general, graphics requirement for trading and Office are very low.
It depends which trading plattform you use and how many indicators on how many charts. Basically the CPU is the bottle neck not the graphics
Generally not true... only in "custom applications" requiring high level of CPU input.... those not pre-programmed to run from RAM.
I say that vecause most laptops use the graphics that come along with the cpu, you buy a cpu with decent power you get a good graphics core with it
No worries. Most software packages are designed to "load into RAM, run from there, and with only minimal CPU involvement". If one's use involves something outside of that routine (like custom calculations/graphics), the CPU get much more involved and may become a consideration.