Yes, the charging connectors are weather sealed, up to a point. They are OK with rain, snow etc, but the connector should not be subjected to high pressure water, say from a pressure washer, when the charge port door is open and a connector plugged in.
You most probably won't get a decent price from Tesla for a trade-in, as they aren't really interested in them, and will only offload it immediately to an auction house. The price they gave me was a couple of thousand less than I got by selling to a dealer, and that was maybe a thousand less than I'd have got from selling privately (I just didn't want the hassle of dealing with loads of tyre kickers).
The price I got offered by We Buy Any Car was a lot more than the price from Tesla, also.