Child Allergic To Certain Foods. Tested Positive For House Dust Mite. Prescribed Medicines. Safe For Long Term Use?

My son is 4 years old weighs 13kg and has been suffering from allergic cold since childhood. Looking at the symptoms my paediatrician had mentioned that my son has child asthma and had prescribed to give Levolin inhaler to be given whenever he got cough and nose running. Recently I consulted an allergy specialist, we took a blood allergy test in which he tested positive for house dust mite, level was 15.6 and the test for food panel (egg white, milk, fish, wheat, peanut and soyabean) tested negative but level was 0.19. He has been allergic to egg, milk, bananas, nuts at some point of time as soon after consumption he used to get rashes on his knees or elbows, pass stools , so we avoid give him these food items.
The allergist for treatment has prescribed Budecort 200 and Nasonex ,1 puff , once a day for 3 months more, we've already completed a 3 weeks course earlier with Budecort prescribed twice a day and Nasonex once a day.
I just wanted to know if it is safe giving the above medicines for a long period and will it affect the child's growth. Also do we need to take any special care with relation to the child's diet.
thank you