They say rightly that the only silly question is the one that isn't asked!

ANA is a screening test and rather important in the diagnosis of lupus. It doesn't say anything about how the disease expresses itself in an individual. A few 'patterns' of ANA can suggest other conditions or other sorts of connective tissue diseases, but many are quite general and are found in a wide variety of diseases not necessarily autoimmune CTD's.
Anti ds DNA will confirm a lupus diagnosis if other signs and symptoms are present but it doesn't say anything about how the disease will in fact present or develop in time. people without anti ds DNA antibodies can ahve severe disease. only half of those with lupus have anti ds DNA antibodies. It is also reckoned to be useful for assessing disease activity or the success of medication but often doctors go more or as much by how the patient is feeling and the results of other tests.
This is why initial thorough and then regular testing is important for everybody whatever antibodies they might have.
There are tests for photosensitivity but they aren't usually done. As you say it is individual experience. Not everybody with lupus is photosensitive and some doctors think the whole question is grossly exaggerated.
Anybody with specific lupus skin problems can assume they are photosensitive unless it;s proven otherwise.
people often feel unwell after exposure to sun and not alwyas straight after. It seems certain that in some people systemic disease is aggravated by sun exposure even if there are no other signs - increased proteinuria for example. Photosensitivity can develop in time and I have read that it can wax and wane like other symptoms. Skin lupus can develop over the course of the disease.
If there are no clear signs of photosensitivity I would suggest taking the sorts of sensible precautions that everybody should be taking these days to avoid skin cancers.
Cheers
Clare