I have a Pi 3B+ I run qBittorrent, Plex, ProtonVPN through Wireguard, and a Samba share on and have had 0 issues. It’s connected to a 2 TB external SSD which is where the Plex media library lives and coincidentally where qBittorrent downloads to by default wink wink. I also have a P2P VPN called ZeroTier that allows me to securely connect to the Pi from anywhere. You should be golden with a Pi 4.
I’ve had zero issues even transcoding 4k BluRay content, but it required adding active cooling to prevent the Pi from overheating. Thankfully you can get a tiny heatsink and fan for under $10.
Edit: Accidentally said RPi 5 which didn’t exist… Fixed.