The bankruptcy protections for retirement funds are largely a matter of state law so any advice in that area would need to be state specific. I do think that keeping rollover funds separate from other qualified accounts is a good idea, though, regardless.
As noted above, tax diversity is a very good thing. The post-tax could be Roth or just non-retirement accounts.
I’ll admit that the case for conversion for this scenario is less compelling than the case for go-forward contributions to a Roth (for someone at age 25).
Whether or not conversion at marginal 22% makes sense depends on your future assumptions about income and tax policy. I think anyone who has had the discipline to save nearly $30K for retirement by age 25 has potential to build significant wealth over a lifetime, at which 22% tax rate will seem like a gift. I don’t want to take this down a potentially political thread, but I do have the opinion that the federal tax rates for 2018 will in the future be viewed as the good old days, possibly as early as next year.