For me the best transfer partner has been delta. For domestic flights if I am flexible with schedule I can get 2 to 2.5 CPP fairly easily. I am not sure how that would fare for you to Hawaii or Japan. What is your home airport? If west coast you will have better deals for those 2 locations than me being in the east.
There are mnay variable to consider, time of year, day, ticket class etc. For Hawaii Delta seems fair at 25K- 45K miles for basic to main, since it's only 6 hours nonstop one could take the cheap rout and go basic.
For Japan though Delta seems kind of high from LAX compared to ANA or JAL, at least 325K for lay flat seat. Which would be nice for a 15 hour flight. Where as JAL and ANA hover around 180K point for Biz Class.
If you planned to fly directly to Japan from Hawaii, you could probably survive Comfort for 75K miles. Lay flat is 420K for some odd reason.
You could always check multi city option which would run about 100K basic/comfort from LAX-HNL-NRT-HND-LAX with the last leg being compfort as it's the longest.
Only having 50K, will only get you to Hawaii and back on Delta. If you're wanting to go to Japan, you'll need more points. Or take the most basic award ticket, and it will be cramped traveling that far in economy. Of course you can always select the miles+cash option, but it doesn't reduce miles needed by that much. Plus you're obligated to fork our more Money.
You could try subsidizing your points balance by adding the Everyday card with the 25K SUB. Personally, since flights to Hawaii are fairly reasonable. I'd just pay the cash for it, and use as many points as I could to lower the Japan trip cost.