I did my sister's front door plaque in 2001 and then again in 2010 using our Clear Woodshield a microporous exterior finish that dries to a satin finish and brings out the original colour of the wood. 2 coats should suffice recoatable after about 24 hours.
Not sure if it's too late but we can tint Precat or AC lacquers to that shade. I've just checked our promatch system here and we have formula.
All we need to know is the sheen level and quantity your are after.
Osmo will definitely tell you not to put anything on the surface that prevents the Polyx from deeply penetrating into the timber so probably best not use knotting solution.
Hope this helps.
I wouldn't recommend a interior varnish be applied outside. It's very likely to crack , blister and flake off causing quite a mess.
Unfortunately I can't think of anything that would sit well on an emulsion paint externally.
2 part PU is harder wearing than 2 part AC but there is not much in it. AC is generally cheaper and is certainly more popular amongst the majority of furniture manufacturers we deal with.
Butanol is the solvent you need to retard the drying of 2k PU...we normally recommend you start off by adding on 5%. In saying that we would recommend you try applying a couple of thin coats using the thinners you have (no more that 2%) and see how you get on.
The fast dry thinners may be compounding the problem, if you are applying a heavy coat? We would recommend no more that 20% thinners and applying 2-3 thin coats.
Although we have no experience with Intercoat lacquers, we do have a large amount of experience with lacquers.
Orange peel generally occurs when too many thick coats have been applied which prevents the solvent evaporation. There are a few options to solve the problem
1. Adjust your spray...
Definitely finish with a wax otherwise the shutters will look very tired quickly with scratches. Applying a clear wax polish using Superfine 0000 steelwool, leaving a few minutes and buff off with a lint free cloth will produce a lovely satin finish...not glossy.