These two will come in handy. The first one is good for more complex recipes. The second one works for complex recipes as well with the help of underground belt.
I actually like the blocking of inserters in a row of smelters. This way my smelters only run, so only use power/fuel when they are needed. This not only saves power but lets me quickly visually see how mu factory componant use is compared to creation. If all of my furnaces are lit up, I am using all the output and need more furnaces, if only the last couple are lit up, I have room to expand, and importanly, if only the first few are lit up, it means my ore/material source is not keeping up(usually mines went dry).
Once I have more than 3-4 furnces of each ore, I spend more time zoomed out to see the big picture so this is important.
I use faster belts on all turns as a habit. Besides this design is simple, but larger designs would kill me trying to identify which belts i need to use.
The difference in resources is negligible too: main reason why I dont make only express belts is due to labeling - That way I know which belts are slow and which arent.