Not every celeron cpu is good for multi gpu mining. I remember from eth mining days when I bought wrong celeron for my 19xpcie motherboard. Celeron G3900 works with multiple (8+) gpus at x1 pcie.
Do not use first pcie slot, IMPORTANT it is x16 and it uses up most pcie lanes.
TLDR: DO NOT PUT GPU IN FIRST SLOT, LEAVE EMPTY
If you are using an x1 raiser, then there should be no problems with 8 video cards on a regular motherboard. And you should also not use NVMe drives.
If there are more video cards, then it is better to think about buying another processor in advance. But for me, the ideal number of video cards on a motherboard is 6, so that consumption is no more than 1 kilowatt per hour.