You've got a good plan started! As a BLU and DRG 90, maybe I can offer you a good deal of advice in this regard.

Now, what you've got going is a good goal, but I suggest that you take your WAR up to 30, not your THF. The reason for this is because your SAM sub, which you're going to want as a DRG unless you plan on soloing the whole time, is going to need a WAR sub when you level it up. Since our final cap is going to be 99, your subjob will have to be at least 49, which means ITS subjob has to be at least 24.

Beyond that, I also suggest you level WHM and RDM subs as well as BLU; each mage sub has its own benefits to the DRG job when using it for solo play. WHM has Cure IV and Divine Seal for emergencies, as well as Reraise, Shell, and Protect. RDM comes with Refresh at DRG82, as well as Protect, Shell, and Phalanx. BLU's biggest advantage is the fast casting rate of its low-cost spells as well as Cocoon, which provides a 50% Boost to your Defense for a short time.

So in short, my advice: follow your plan, but also level SAM, WHM, and RDM subs at least for DRG.

Also, as a side note: get NIN as a subjob for BLU while you're leveling it as a sub.