[warn] Your computer is too slow. . .
Raspberries are cute but seriously underpowered for crypto-intensive applications such as Tor. You can (any/all of)
1) ignore the warnings
2) restart the relay to send-off any hidden services that might be causing the overload
3) buy a dirt-cheap used laptop or mini-tower on eBay to run the relay
4) buy a Beagle Board if you enjoy fiddling with miniature computers --much more powerful device
The configured limit is reasonable for the device.