Sweet yeast-dough too yeasty
It’s too yeasty because you are putting too much yeast in. Yes, the majority of recipes states one 7g sachet per 500g, but that will give you a yeasty taste. It will also give you quite quick results.

As a first step, I suggest you consider a cold rise - reduce the yeast to 1-2% fresh (or about 3g of dry yeast), use cool instead of warm liquid and let the bulk rise (first rise) happen in the refrigerator or very cool room. Alternatively, let the dough “spring to life” on the counter for about an hour, shape your buns, brush with milk and put them in the fridge overnight. This will significantly reduce the yeast flavor.

For texture, 50% hydration is quite on the dry side. I would go up to at least 6o%, so 300 ml, maybe a bit more. Also, don’t melt the fat in the milk. Yes, many recipes suggest that,  and it works. But kneading without fat first until the window pane stage and then incorporating the fat will give you a lighter texture, which will also help with the crust. 

Don’t brush with egg, for a softer crust, try pure milk or an egg wash with milk in it. Bake with a generous amount of steam to keep the crust even softer.

And when you are ready to take your buns to the next level of fluffiness, consider a water roux (aka tangzhong or Mehlkochstück).