Gigabyte B450M S2H paired with Ryzen 5 3600 works fine.
Gigabyte B450M S2H paired with Ryzen 3600 is fine. Your GPU will be GTX1660, and you're planning to upgrade to RX 5700 XT next year.
Hello there! You seem fine, but I’d pay extra for a pro4 or pro4-f version.
The board can manage a six-core setup without issues.
You're good as long as your CPU stays at six cores or less and 65 watts or or less.