That's fine. German support can also help.

Which LED do you refer to? When the LED is solid on, can you get internet access from the modem? You can check the user guide below to know the right status for each LED....

You may try to restart the router, try a different browser, clean the cash, also try a different client? By the way, the model number seems not right.

If you can put the router in the middle of the 4 rooms, you can buy an normal router, like archer C7. But if the router can be only put in a corner in the house, you will need to a good router and a...

Your issue is quite weird. You can send an email to support@tp-link.com to do more analyze.

What's the wifi monitor? Is it the speed showing on the monitor the link speed between the PC and the router? If it is, the speed is also limited by the network adapter on the PC.