We have a quad HDMI capture card and regularly use 3 HDMI cameras, 1 Logitech C902 web cam and 1 PTZ Camera via NDI. This is our normal configuration for live streaming our 4pm mass on Saturday. We operate from the balcony in the rear of our church. Our church is relatively small with a limit of 600 occupants. The C920 is mounted on the balcony rail fixed view down the main aisle and used for procession in and out. 2 of the via HDMI are Canon R800 on tripods with static picture. One is fixed on the altar with a wide shot covering the ambo on the left of the altar to the priests chairs on the right. The other is a static view of the priest's chair. One PTZ camera is mounted on the balcony center looking down the main aisle and controlled from OBS via the PTZ control plugin. The 2nd PTZ camera is mounted on a tripod to the right side of the balcony, also controlled in OBS and its video is picked up via NDI over our internal network. In addition and on occasion, we use 2 old android cellphones 1 running Droidcam OBS and the other using IVcam. So at times we have had 7 camera sources active in OBS. works quite well.
Of course the PC configuration is important especially the CPU / GPU then at lease 8gb RAM. We started with a Ryzen 5 then moved to a Ryzen 7 which doubled the number of processing threads, gave us a better GPU and now our video is smooth without the least stutter. I also added 8GB ram and turned on Dual Channel memory in the BIOS which also increased processing speed. I learned that from a gamming youtube video. Hope this helps.
