3) No. Pretty much the same answer as #2.
4) Yes, TurboTax should be able to handle it. Just be sure to maximize the 330 day Physical Presence Test by choosing the best 12 month period (such as September 2017-September 2018, which puts more days into the 2018 year).
Adding a little SU TaxGuyBill's answer, -- note one item 1 above. Whereas you can find a period to qualify for the FEI Exclusion, the actual amount eligible for exclusion would be reduced because your foreign tax home would cover only Jan 2018 thru July/Aug 2018. From the time you enter the USA ( or 35 days thereafter ) , your income ( even though from a foreign source and taxed by the Foreign country ), would be only eligible for foreign tax credit. At the same time , I suppose one could make an argument that sabbatical pay is really based on work done during the prior X-many years and therefore is eligible for FEI exclusion --- have not seen caselaw on this . This is my opinion
I agree with all the other responses by SU TGB