The RAWs are only 20MB, I meant the final image after you are done processing them. The PNGS are like 60MB, but I guess the JPEGs should suffice but there's so many options I don't know whether they really matter.
Also, is there a benefit from converting your manufacturer's extension to DNG?
Ah ok. PNG isn't great at doing lossless compression so that wouldn't be my first choice. If you really want to store a non-raw format while keeping the original quality, TIFF with ZIP compression is not bad (still lossless). Quality 75 JPEG is good enough for most of use case. I use quality 85 or so for print if they don't take other larger format.
The benefit of converting to DNG is a bit situational. It's probably not worth it for most of the people since manufacture raws are well supported by majority of software.
First of all, it is open standard format so that's good in its own way. The real benefits are: 1) If you use separate program for different parts of processing and want to keep a raw format. I prefer keeping a raw format because when a software opens a raw file it implicitly operates in non-destructive editing mode whereas they will happily overwrite a TIFF. 2) If you use LR, DNG files don't have side cart files -- it embeds the side cart information in the DNG so it's a bit nicer from file organization point of view.