Hi Poco-poco
If I am not mistaken, you can apply for BPJS through 'Jalur Mandiri if you are KITAS/KITAP Holder, even if you are not working.
Syarat daftar bpjs untuk warga negara asing/wna (pegawai atau mahasiswa asing) yang sudah tinggal di indonesia minimal 6 bulan wajib
www.pasienbpjs.com
I'm not too sure about your question regarding pension: how do receiving pensions work if you don't even reside in the country (others might help answering). If you are talking about Indonesia, you can definitely open a bank account as a foreigner in Indonesia.
https://finansial.bisnis.com/read/2...bisa-buka-rekening-di-bank-bermodalkan-paspor
If you are officially employed in Indonesia, then you need to get NPWP (again KITAS/KITAP holder allowed). Regarding declaring tax overseas, I guess it depends on the tax agreement between that country and Indonesia. In general, I think you still need to declare how much taxable income you earn overseas to your country of residence into the assessment.
Hope it helps.