Re 1) It is useful to keep exploring other means of treatment because at some point you won't have antibiotics left. You want a secondary method that can be deployed instantly once the primary fails. Currently cryptographs are developing Quantum-Computer-resistant cryptographic algorithms not because there is a quantum computer that can crack RSA but because a quantum computer that can is in the not to distant future and if it exists then we need immediate replacement.

Re 2) I don't think that would be a problem considering together with 1 there will simply be a need to develop a quick but reliable method to test for which collection of phages work, probably even develop cocktails of phages for a more broad application. Reducing the amount of antibiotics used would also help reduce the risk of the broad spectrum antibiotic failing because of resistant bacteria.

3) Phages are living things depending on who you ask. Phages are rather simple and will to my knowledge remain viable for a good and long time. Antibiotics may be inert but also have an expiration date, you can't just use an 60yo antibiotic and hope that works. At some point the contents of the antibiotic will have broken down and oxidized.

4)Fair but apparently people have been using it in the Eastern Block for a while with some success. There are some shoulders to stand on and continue R&D.