Surpin
100mm stem with 15mm spacers is 100% normal, no need for concern. That's probably close to how 99% of bikes are set up at the factory. 110mm stem and 25mm of spacers are also totally normal.

Your body only 'sees' three points of contact - the saddle, the pedals and the bars. If you can get these three points in relation to each other such that you can ride comfortably without maxing out any adjustments or using oddball parts then I don't think there is an advantage to use a bit shorter stem or a bit longer stem, as long as the end result is a well-fitted bike. If you needed to use an extra long like 160mm stem, there could be some concern that this will put your weight a bit further forward than the manufacturer intended and the handling of the bike might not be ideal. And there might be other considerations depending on your intended use of the bike - for instance, a mountain bike used for very rough terrain often has a smaller frame to allow the rider more room to move around to balance and position the bike on the trail and overcome obstacles. But this is less important with road bikes as you are often sitting relatively still and cranking on the pedals, and the shape of the frame connecting the saddle, pedals and bars is less important.