RBK50 replacing AC1750, with a few new connectivity problems

I recently changed from an AC1750 router to the RBK50, and am unable to  connect to my older iPad and to my ethernet printer using wi-fi.  I'm in the US, and am using an ISP with its own propriatary TP-Link router, which I then hook to my router and then to the Dell Inspiron desktop computer.  This is exactly the way I hav=d the previous AC1750 connected, and everything worked fine.  Now I can communicate fine with my desktop, my smart TV, my iPhone, and my laptop Dell computer.  Also I was able to set up Echo Plus.  However, I have not been able to set up my wi-fi printer (Epson Ecotank 3750), my Amazon Echo (early model), my Echo Dot, and my older iPad, all of which worked well with my prefious Netgrae AC1750.. 

I am not a tecchie, but I can follow clear instructions that don't consist of geekspeak. 

Thank you for any assistance you can provide.