Hi Boombod - if you make your title more specific then you may get more replies from women on this regime.
There is some research which shows that oral not transdermal oestrogen can affect levels of thyroid hormone available in the body (for some women) so a review after 3 months can be recommended to test your thyroid hormone levels in case they need adjusting ( I would push for this anyway even though you're using transdermal oestrogen).
In terms of flushes - it depends whether your flushes were controlled with the Evorel? If not then hopefully the gel will work. It should take affect pretty quickly re flushes - you should notice them lessening in frequency within days, hopefully.
I hope this combo works for you - and the Mirena should definitely help with the heavy periods once your body is acclimatised to it.
Hurdity x