So confused by your description. There is only one Ethernet port on TL-WA701ND, so there is no division of WAN/LAN port.

Refer to the following link to set range extender mode on TL-WA730RE. http://www.tp-link.com/en/article/?faqid=357 this will help you receive wifi from 7800N and transfer internet to your NAS by a...

Repeater uses four-address and universal repeater uses three-address. Some devices can only support three-address so universal repeater is commonly used. The easiest way to check whether the repeater...

It seems that you shouldn't enable WDS on TL-W8951ND. You can only try universal repeater on TL-WA901ND to repeater wireless network from TL-W8951ND.

Make sure your network adapter supports roaming feature.If you’re not sure, upgrade the network adapter’s driver to the newest one and try again.