Belgium
Macedonia
Netherlands
Moldova
Estonia
Greece
Finland
Armenia
Belarus
Hungary
Romania
Georgia
Russia
Serbia
Albania
Denmark
Belgium is the clear choice to start. Anything else would be inappropriate (Estonia or Finland) or a total drag (anything else.) Finland is toward the middle of the semi because I feel like it would be most fun to lull viewers into a false sense of security before surprising them with it. The second half is pretty easy and I think there are a lot of orders that would work as well as the one I came up with. Denmark last is an honest prediction, NOT a personal preference.
Lithuania
Malta
Czech Republic
Montenegro
San Marino
Norway
Portugal
Ireland
Sweden
Poland
Azerbaijan
Iceland
Switzerland
Slovenia
Cyprus
Latvia
Israel
I kind of gave up on the first half, but I'll be surprised if anyone other than Lithuania or Malta opens. I put Sweden at the beginning of the second half, because the first half will be dragging by that point and something upbeat and familiar will be welcome (it's not like putting it there will hurt it.) I almost chose Latvia to close because of course I did, but I looked at the last couple of years and it looks like the song that closes the semis should be uptempo, and preferably a silly one if you have one, so that's obviously Israel.