Hi Mik, welcome to the forum and congrats on your new feathered one
I would like to say that if you think there is a chance your new guy/gal is sick then see an Avian vet.
If the store where you got him offers a free checkup, then by all means use that!! If not, then take him to another Avian vet for a checkup.
While sneezing is not always a sign of illness, they all sneeze occasionally just like we do, if it is done excessively or is accompanied by fluffing and or wetness or staining above the cere it IS a sign of illness.
I am not there to observe your bird so have no way of knowing just how often he is fluffing up, or how long he remains fluffed. Fluffing is a normal thing too if doing it before a nap or sleeping, or maybe fluffing quick to rearrange feathers or shake something off.
But remaining fluffed for extended periods of time is a sign something is off.
It is definitely not too cold in your house.
By any chance have you been supplying your new bird with millet spray? Spray millet is notorious for being dusty which may cause sneezing and also the hulls can get in to their nares and cause sneezing and other complications if the sneezing doesn't remove the hulls. SO if you are offering millet spray I would remove it. It's really not good for them especially if they are eating only the millet spray and not their seed mix or veggies. They get plenty of millet in just about any seed mix you feed anyway.
My motto is if in doubt seek medical attention from an Avian vet.
So if you are unsure of whether he is sick or not...get him checked out. The sooner the better with these guys.
Oh, you say you also have finches? It is very important to quarantine new birds from your existing birds for 90 days.
Even if not housed together in the same cage, illnesses can be transmitted in the air..esp if sneezing?
So be sure your new one is a separate room from your finches.
As far as the cage goes..I think it is fine. It is a good size for your one guy/gal. Especially if you plan on letting him/her out for fly time once s/he is trained.
You might at some point down the road want to go bigger so you can have more toys and feeding stations etc without overcrowding. You'll be surprised how many toys you will end up accumulating. LOL
Here is a link for reading your bird's body language you might find helpful.http://littlefeatheredbuddies.com/info/gen-bodylanguage.html
Lots of other useful info there too if you click on different things in the sidebar...look around
I forgot to address the scratching his cere..how often is he doing this?
Anyway, if I were you I would take advantage of that free checkup. It would be nice to get a weight on him anyway, and an overall stamp of good health.
If he does have some sort of infection going on then it is always best to get treatment asap before it is full blown.
I always like to recommend getting Herb Salad to new members. It's a great product with many benefits. Most birds seem to like it. Even picky ones
Check it out and be sure to read all about its benefits. Again, click on the sidebars..What makes us best..comments, Q&A's..http://www.twinbeaksaviary.com/herbsalad.html