I used to work for a company whose setup was super simple.

ADSL Modem > Firewall > Router > Web/DB servers

It was basic, but it worked. Our web servers were mission critical, but as a B2B business they, and the ADSL connection, didn't sustain a heavy load. The only issues we had over several years were with the ADSL modem. Everything else just worked.

When we moved office we moved our servers to a co-hosting centre with an upgraded network setup with all sorts of backup and redundancy. Every week something went wrong. Sometimes simple is best.