Great work tackling this old 401(k) rollover head-on, cancelthesky. I just went over this rollover process myself (I detailed it another thread over in the Investment board, in case there's any info here that might help you):
https://forum.mrmoneymustache.com/investor-alley/getting-out-of-ameriprise-help-me-move-past-the-face-punch-stage-into-action/Note: I was doing an IRA-to-IRA transfer (not a 401K-to-IRA transfer). But I was also rolling over to Vanguard so I think the basic process is similar. My advice: Call Vanguard and ask them for assistance. They helped me set up everything electronically, then they sent me some forms to fill out. I then sent the forms back to Vanguard, and they are now in the process of working with my old investment company to transfer over everything. I'd been putting it off for awhile thinking it was too overwhelming, but once I swung into action it was all really straightforward.
Once the funds are transferred over to Vanguard, I'm going to do an 80% VTSAX (Vanguard total stock index) / 20% VBTLV (Vanguard total bond index) allocation of that IRA. JL Collins of THE SIMPLE PATH TO WEALTH fame would say I'm being too conservative and urge me to put 100% (or close to it) into VTSAX, but this is the allocation that feels most comfortable me right now.
Nice job with your 11% pretax going into VFFVX -- I also really like the Vanguard target-retirement funds. I've decided to use similar Vanguard target-date funds for my 401(k) at my current job, and use Vanguard total stock / bond index funds for the IRAs from my old jobs, similar to what you're planning.
Re. the Roth IRA / tIRA tipping point question: I wonder if it makes sense to re-evaluate in December 2018. You can fund a 2018 IRA (either Roth or traditional) until 4-15-2019, so you can wait and see how much overtime you earn in 2018 and what your total salary is, and then decide from there which IRA option is optimal. Also, if you are worried about hitting that Roth IRA salary limit, it looks like you have room to contribute about 6K more to your 401(k), which will further lower your MAGI. Good luck.