Connecting multiple gpu

My rtx 2070 is now installed on my computer. This is not enough for quick work.
If I buy another rtx 2070, will it be right, will I see accelerated work? For my code to work at least somehow quickly, I need at least 4 video cards according to my calculations.

Who connected several video cards give me advice.

Do I need to use SLI - NVLink to connect video cards or can I just use PCI?