I say do it. Normally I do not like to trade starting value for depth but I think in this case you need the RB depth enough to start the season to trade for this. . PPR or not I think either way I'd still make that trade. You will need Rice having Lynch on your team. Edwards is in a contract year so I expect a better performance out of him for sure this year. Driver is also a good #3.
Not a huge fan of your RBs and I don't think R Rice would improve your team all that much (especially losing AJ). I think you have enough WRs to keep your team in the hunt as well as the best (prior to the season beginning) QB. I say wait it out and see how your team stacks up the first couple weeks.