I agree that starting you on the maximum licensed dose seems odd. 50 mcg is standard and you gradually increase from there if you need to, based on your symptoms, after, as Joaniepat says, 2 -3 months at each dose. This gives time for your body to adjust to each level and time for you to see if it is sufficient to control your symptoms. When I started on HRT, I tried to increase my Oestrogel from 2 pumps to 4 pumps in one go, in a vain effort to control the adverse effects from the Utrogestan. It didn't help and I felt very nauseous and I was told by the consultant that the sudden increase was the reason why. I gradually increased to 4 pumps over several months, and had no more nausea that way.
If you are perimenopausal still, then the hormone levels in your blood are still going to vary a lot, hence the variabiity in the tests.
You don't have to have oestrogen with the Mirena but I wouldn't personally want to have synthetic hormones in my body for an extended period of time if it is serving no purpose, unless you are using it for contraception. I would keep it in whilst you are deciding whether you are going to continue with HRT though.
As for patches versus gel, it's about personal preference really and how well you absorb from each product. Patches irritated my skin, so I switched to gel. The drawbacks are having to take the time each day to apply it, wait for it to dry and decide whether you are going to apply it in the morning or night time or split the dose. You tend to get more peaks in blood levels with gel whereas patches give a more steady release but I can't say that I notice it.