American Amazon is full of metric magnets.
You can buy alot very cheap.
A Pro balance kit - Adds 200 grams to the rear to balance the weight. https://www.ebay.com/itm/Valve-Index-Pro-Balance-Enthusiast-Kit-200-Gram-7-Oz-Studioform-VR-Direct/154127876149?hash=item23e2bcc035:g:~Q4AAOSwTzlfab0U
Lens covers - Protects the Lenses from Dust and Sunlight when not in use.
https://www.amazon.com/gp/product/B07VS627FK/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1
A storage solution - The box the index comes with is massive. You'll want a way to store it. Internets has some options.
5mm x 1mm disc magnets - These can be used to tilt the display to achieve the best viewing angle. https://www.amazon.com/gp/product/B07C5HXR2X/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1
Chilldex - If your intended play space gets hot when using the index. https://chilldex.com/
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The base stations come with equipment necessary to place on a shelf, table, or mount to the wall. If you prefer a stand look into light house stands. You'll want to place base stations in places where they won't see reflective surfaces. Like a large TV or a window.
If you are use to high fidelity, manage expectations on picture quality. Games on a monitor are not going to look better in VR. They will be more immersive and 3-dimensional but jagged edges and god rays will be expected. It will take time to find the most comfortable fit.
Get FPSVR so you can see the frame rate and how much your GPU is pushing. You'll want to adjust the frame rate and Supersampling to achieve stable frame rates.
Start with games that are made for VR only. These games take the experience to the fullest. Superhot VR is a must experience in my opinion.
If you want to play any Oculus exclusives. Look into Revive, this will allow you to play Oculus games on your index.
Welcome and Congrats.