Can the NSA or similar agencies see where my device is when using Tor? If so, to avoid this, do I need to encrypt my wi-fi as well?
NSA has different methods to discover location of server. You can read this: https://www.eff.org/files/2014/01/06/20131230-appelbaum-nsa_ant_catalog.pdf
You need to differentiate two attack vectors.
One is NSA or whoever looking at the traffic originated by you that spits out from some Tor exit node.
Another one is NSA or whoever looking at traffic you interchange with your WiFi access point and with your ISP.
In the first case you are practically safe, unless you make something that ties that exit node to you (like using your Facebook account).
In the second case they will know you are using Tor, but will be almost unable (almost is important here) to grasp wchich sites you are browsing through Tor.
Having unencrypted wifi in general is not a good idea. The FBI has taken people down by monitoring their unencrypted wifi and simply sniff out what ip's you are connecting to from the network, they can then simply check it against the tor network's public ip database, then they know if you are on tor. Also ISP can see that you are connecting to Tor, but not what you are doing over that connection. so you can easily be detected as a Tor user.
Also you do not specify what device you are connecting from, if it's a cellphone then they know regardless because your cellphone connects to the cell-towers even if you are on wifi using tor, and then it's a matter of triangulation