How do. I am studying Tagalog as an inroad into Malay/Indonesian. My reasoning is that, as an Austronesian language, the grammar will be comparable, so if I get the hang of Tagalog (which I expect will be easier than Malay due to the large number of Spanish and English loanwords lessening the vocab load) Malay should be a snap (comparatively). Additionally, I don't know any Malaysians or Indonesians, but I know several Pinoys and they all have a comfortable grasp of Tagalog as they speak it at home.
Native Malay speaker here, Tagalog has a lot more grammar rules than Malay/Indonesian that you have to follow so I can definitely confirm if you can get the hang of Tagalog, Malay/Indo will be easier for you