I suggest WNDR 3700v4 it has 128 MB RAM/ROM, USB, 5 GHZ WiFi and you can get for ~20$ on ebay. It's a good toy. I have it myself and it works great. I have many services on it. Openvpn server, adblock, dnscrypt-proxy, transmission, NFS server and so on. It works great for me. I have about 15-16 hosts in my network.
I'm no expert, but regarding the TP-Link C7 for 80€, I think a much better choice would be the TP-Link C2600, which can be found for as little as $80. The specs are much better, and I've been using one for a while (purchased like new on eBay for ~$50) and have been very happy with it.