@mamiwhereru 

If the ax55 works the same way as my ax72 does then what your asking will work. 

I have 3 ax72 routers at my property and I have 2 of them in AP mode and one as my main router. 

All my routers are set up the same as in same ssid and passwords so I know that no matter where I go around my property all my devices will connect using the same credentials and I won't have to input different ssid and passwords. 

I've also done the same for the guest and iot. 

You should be able to roam between routers but you must keep in mind that some devices don't like switching automatically so you may have to turn the wifi off and on again depending on devices.  

I have a 2 story house and one of my ax72 routers (AP mode) are up on the top floor to help cover the top floor of my house plus it helps blanket from the front of my house outwards. 

I have a ax72 (main router) in my kitchen that sits on the ground floor and is about middle of my whole property layout that covers my whole ground floor and most of my garden. 

My last ax72 sits in my man cave at the bottom of my garden Covering parts of my garden and then some out past my boundaries so as I approach/leave my property I can still have WiFi to a point. 

You shouldn't loose any speeds as they'll be connected by ethernet so what ever your main router is able to put out from your isp at that given time is what you should get at the other ax55 in AP mode, 

I've never noticed any major speed differences in my set up between routers

I'm fortunate enough to now have fttp and im on 1gb down by 110up and when ever I've walked around my property doing random speeds checks, I vary between 870/110 upto 940/110 on all routers at the same time depending on the time of day. 

Hope this has answered some of your questions 

Chris 👍🏻