If you tap with a M5x.08 you are running the risk of the screws pulling out since there won't be much left for the screw threads to grab onto. If you are going to drill them out some more anyway, try it and get some blue loctite for a little extra insurance.
I think a better plan would be to put an M5x0.8 helicoil in there. These come in kits and it will tell you which size of drill bit to use, it might be a metric bit, or maybe a fractional or number bit, you'll have to check.
I've got an older French Zefal Husky floor pump that has fine metric threads on the hose. Recently I got a Topeak replacement hose with an adapter kit that claimed to be suitable for Zefal. Not this zefal apparently. I'd llke to be able to find the appropriate threaded brass pump fitting to work with this new hose.