ESA and Universal Credit transition questions

Hi, I hope one of the mods can help with these questions...

I'm currently on income-related ESA (SG) and understand universal credit is getting rolled out in my area later this year (Sept, I think). I am wondering, well, worrying, about when I am likely to be expected to make the transfer and what's involved... I saw on one site that those on sickness benefits will be likely to make the transition last (after JSA/ HB/ other benefits etc) and that those on ESA won't have to undergo the process until 2019, with an expectation all those on ESA benefit will have been swapped over to universal credit by 2021. I also read that they will transition ESA WRAG first, then those in the SG. Is this accurate? This info was just in a conversation thread on another board (not a member of it) and was a couple of years old so I don't know if this is true or not.
Is UC roll-out running to timetables, even?
Also, I don't know if it will be the case for me but what happens if a new assessment (ESA50 and medical) happens just before the changeover from ESA to UC is due, or even coincides with it? Would you be required to undergo two assessments? One for ESA and then another for UC? Do the sick also need to wait the 5 weeks (I think I heard) without money while the changeover happens.
On top of other conditions, I have horrible anxiety and this stuff (the unknown) around changing from ESA to UC...the whens, hows etc are making that a lot worse...

Thanks.

Hi Gordon, thank you.
I'm wondering if some ESA reassessments could've been delayed purposely to tie in with the changeover to UC. As you say, the DWP are not known for a logical approach so it would seem unlikely, but they are a law unto themselves.
My concern is, if that's not the case and it fell so that an ESA reassessment was done right before UC was due to replace it, would the claimant then be expected to undergo the assessment process again under UC rules...potentially forcing two assessments on a claimant in a very short space of time?

I've read nothing to say that UC in my area will come in later than stated on the official list...not sure where I picked it up but I actually thought the roll-out was running ahead of schedule. There are delays, then and they're actually running well behind schedule?

I've seen some here speaking of being in the process of making the transition from ESA (I think) to UC. I assume the changeover schedule varies according to where you are in the country and perhaps your other benefits like Housing Benefit etc.

Thanks, Gordon.