Associated fields

I don't really recommend this if your site has a lot of users as you could end up with a dropdown with thousands of options.

Should this be ok for a user table with around 200 - 300 users?

I suppose, but that's still 200-300 options to select from for a dropdown. That's a pretty substantial amount.

Is there a better way to ask the question "who's your best friend" with the site members as your options.

I would just use Connections and provide a Connection Type of Best Friend so they can connect to that user then set their type to Best Friend. Aside from that a standard text field to supply their name manually would probably be fine, which you could then validate it against _users using CB Query Field and its Query Validation.

I would just use Connections and provide a Connection Type of Best Friend so they can connect to that user then set their type to Best Friend.

Using Connections sounds a good option.

Aside from that a standard text field to supply their name manually would probably be fine, which you could then validate it against _users using CB Query Field and its Query Validation.

Can the text box incorporate auto lookup of user names (when user starts typing)?

Can the text box incorporate auto lookup of user names (when user starts typing)?

No, we've no auto complete functionality at this time.