Buying a new pc for mount and blade 2: bannerlord help needed.

[caffeinade]

If you are just going for 1080/1440p then it may be worth looking at the RX Vega 56, GTX 1070, or perhaps a GTX 1060.

I am not sure how CPU bound the game will be but I recommend getting a Ryzen chip.
Either the R5 1600 or the R7 1700.
The gaming performance is slightly less in some game compared to their Intel counterparts, but they offer greater overall power in multi-threaded applications.
In benchmarks the Ryzen chips do perform slightly behind, but remember real life situations are not benchmarks.
A real world system is not just running one game and nothing else, most people have many windows open in the background and this can decrease the overall effective performance of the Intel chips.

General use tends to favor the Ryzen chip's increased thread count, with Ryzen (1600 +) chips offering much better multitasking, and therefore tend to be more responsive in my experience.

I don't know how well Mound and Blade 2 will scale across multiple cores, so bare that in mind.

Intel are also going to announce their 8th gen chips in a few days, they are rumored (or confirmed) to bring 6 cores to the i5 and i7 lines and may offer competition to Ryzen's higher average core count.