Is a saline nasal spray safe to use with asthma and allergies? Thanks.

Absolutely. Saline irrigation of the nose is safe and effective. I encourage all my nasal allergy patients to rinse their nose. There are also non=allergic forms of nasal disease as well as chronic sinusitis, where nasal irrigation is crucial.
Yes. Some people will find that nasal saline irrigation is more effective than prescription medication. Different delivery devices can be found at your local pharmacy and your pharmacist may actually be able to help you choose the right device for you.
Yes. Yes but try to keep the saline as clean a possible.