HI, I enjoyed the ADK plugin for eclipse java, uploads and debug outputs over my usb charge cable (samsung tab2)
a)there are lots of bluetooth terminal apps on goolge play, for just raw bytes, maybe ascii
bcd) i'v never dealt with/seen a chart object/file but im sure you could do your own. In any file, its really just how you code your array & data, if that file type is common , that just means theres a common encryption method. But really when you do your own files for software with new extensions , your load method really is based on the save method , ie does you save data use just temp1,temp2,temp3 or do you save data as time1,temp1, time2,temp2 ect
with my experience learning java, the real trouble i had was really using objects, ya lang changes a little but lots of examples on web,
I found it hard to design, and edit my main windows, but plugins ie..like the bluetooth stack connections were extremely easy.
My first app was Bluetooth data port related, where i Rx numerous values, and TX some as well, took about a week or 2 to learn the lang and develop app. To me it was alot like using vb with a few differences... but thats just me