1. If cost seg gives you more deductions that you can use in the year the study is done, yes, you can roll it forward until you use the entire amount.
2. Current rental becomes your primary residence...you need to discuss this with your CPA/tax professional. You may have recapture tax to pay but it should be less than the original amount you received. Also, you will not be entitled to on-going depreciation once you move back in.
3. STR - This is a complex question and timing, occupancy date, and what is being done in the rehab process are critical to answering your question and guiding you in the right direction.
4. There are no bad questions! Everyone has to start somewhere. When you do a 1031 on a property that you have done cost seg on, you will not have to pay recapture tax. At the same time, you can do another cost seg on the difference between your relinquished property and the new purchase in most cases.
5. I include the expected ROI in my estimates. Talk to your CPA/tax professional and they can give you this information based on the study you received.
I hope this helps.