1) Don't know all your details, but sounds like you can be putting 2x $5500 in a year into a Roth. If one of you is stay-at-home, then you could be doing a spousal traditional IRA, but you provided the scantest of details to go on.
2) Roth vs. taxable is a trade-off. Roth is tax free coming out, but getting at it before 59.5 is a hassle. Taxable counts against you for things like college aid, and has no protections in bankruptcy or a lawsuit, but is very flexible for withdrawals. "Tax free" is less of an issue if you are in a modest retirement, as if you stay in the lower tax brackets your long term capital gains rate goes to zero.
3) Nothing. Existing Roth balance is there, and the principle is accessible whenever needed. The hassle of a Roth ladder is the first 5 years where you need to live your life while waiting 5 years to start withdrawing your rolled over Roth principle. Having an existing Roth balance with some principle to pull out plus a taxable account is what you are likely to have available to live on for those 5 years. Any gap in available funds vs. spending might have to be plugged with IRA/401k withdrawals that would come with 10% penalties, which is what you are trying to avoid in the first place.