As I know, TL-PS310U may be compabile with multi-function printers with scanner function. Check compatibility list here. http://www.tp-link.com/en/products/details/?categoryid=&model=TL-PS310U#down

What ports are you going to open? Follow this, http://www.tp-link.com/en/article/?faqid=205

Did you set total upsteam/downstream bandwidth first and save it?

Mode switch on MR3020 is 3G/4G? Check default gateway on your PC connected to MR3020.

Can you detect any other networks using 7210？ Reset 7210 and you can place 7210 next to 5210 to test if it can be detected.

Not all wireless clients can detect 5GHz signal. You have to ensure the wireless cards of those clients support support 5GHz band.