It sounds like a reasonable first appointment and it's good you have a follow-up scheduled. Some docs dismiss things outright and don't want to see you again
It sounds like he is going to follow your symptoms and try and work out what is going on which is good. I'm not sure what he meant by saying even if you do get a diagnosis they may not treat you? That would be most unusual not to start someone on a disease modifying medication like Plaquenil.
Has anyone done a urinalysis on you? That's another important part of diagnosis as sometimes there are problems there that would count as criteria but may not necessarily be giving you any symptoms right now.
Erythematous means red in medico language
So at this stage he has at least documented it but isnt committing to what sort of rash he thinks it is. If things go on for a while without further committment from him then seeing a Dermatologist whilst your rash is very active and possibly having a skin biopsy might help in diagnosis. If the biopsy comes back positive you definitely have some kind of Lupus, but it can come back negative in some and it doesnt mean you dont have Lupus.
A tricky disease to diagnose in some, see how your bloods come back and keep documenting your symptoms and any further rashes. Will you get results prior to going back for your next appt? See if you can at least then you will have time to understand them and you might have some relevant questions for him. It will also be good to see what he has tested, that helps us to realise if they are being thorough in their testing and know what they are talking about.
Let us know how you get along.