Save yourself some money and only get one video card as performance boost you may get with SLI isn't really worth the cost. Hereis just one article on the subject. Do some research on the subject before you take the leap. Also keep in mind that not all games support SLI.
You might be happier with a single RTX 3070 ti.
Go to the userbenchmark web site to get an idea of how other systems compare to what you're building.