Shooting into the sun

Hi,
I'd like to redo that shot as attached and I'd be grateful for hints and reports about your experiences what to expect.

I already managed to get that shot more or less but I want the sun slightly lower behind that building. The constellation only happens four times a year (there's a second location to shoot from). I had attempted this quite often but failed due to weather conditions. When the sky finally was clear I found that it was roughly three days too late. I don't want to fiddle with filter holders during a constellation that lasts only seconds. For that picture I used a 3 stop ND grad filter. During post procesing in Lightroom I created a HDR with different exposure values of the same shot.

During my last attempts I used a 10 stop ND filter and liked the result more. The color cast was minor but there is some flare. Would you recommend filters at all?

As it's impossible to balance the sun with flash etc., is a silhouette all I can get? How would you critique my image - is that all to be expected or is there still room for improvement?

Kind regards,
Wolfgang