Hi.
If i set up hAP ax² in 1 st. connected to ISP, and another in the basement could these create a singular WIFI
Not sure if i made myself understood.
but the goal is to improve wifi and connection components to ethernet in the basement.
Yes!
Configure one wifi interface as station and the other as ap.
Add both and the ether port(s) to the bridge, then you have the basic (and from there you can configure all wireless settings).
Thanks for the reply 
I was thinking to start my Mikrotik ecosystem with the hAP ax3.
Then further expanding this with RB5009UPr+S+IN, to be the main router, add cap AX in top floor also RB260GSP to connect components to ethernet, move the hAP ax3 to the basement, to expand wifi and connect components to ethernet.
maybe it’s better just to stick with hAP ax² as a starter and keep the budget not flying out the window.