If I were starting again the first few things I would get are:
Foundation + brush. The brush is necessary for me but you may be comfortable using your fingers or makeup sponges, both of which are cheaper options. My first foundation was from CoverFX and was extreme full coverage which I needed at the time but as soon as I made progress with laser I switched to MAC Studio Tech, which was less extreme. Later I started using Kevyn Aucoin's Sensual Skin Enhancer, which is a really fabulous product for full-coverage yet natural-looking makeup, though it's pricey. It's definitely worth it to approach a salesperson and have a conversation about your skin type and needs and not only will they be able to recommend a product, but they can help you find a color match as well. Sephora can be a good place for this because they carry a wide array of brands. For a brush, there's a brand called Real Techniques that makes really nice, affordable brushes that can be found online and maybe in stores too, not sure.
Powder, to keep your foundation in place. The first one I ever bought was Ben Nye, which is cheap and decent enough quality to be found in many professional makeup artists' kits. Elf makes a really nice, affordable one too. You can get some inexpensive powder puffs or spend money on a brush, your choice. I like to splurge on makeup when I can because it makes me feel pampered.
Contour, which can be a trans girl's best friend. The first product I used for this was a very neutral taupe eyeshadow. It's really important to use the right color for your skintone and to not go overboard, and might be more trouble than most people are willing to fuss with, but knowing my hairline and jaw were contoured down really helped me make it out of the house a lot of the earlier days in my transition.
Good tweezers. You don't have to go nuts with your brow game but keeping them neat is helpful. And there's nothing more frustrating than fighting against a flimsy or imprecise tool. I like Tweezerman.
Mascara will do a lot for you. I'm not super picky about mascaras, though I agree with the above note that volumizing formulas are more flattering than lengthening ones.
You don't even NEED all of these things but it's a pretty solid starting point for normal daywear makeup. The next thing I'd add would maybe be a lip liner in a natural shade and some chapstick. I'd start simple and add fun things like lipstick and eyeshadow as the mood takes you. Good skin care can make an enormous difference in your appearance and in the look and feel of your makeup too. I spend crazy amounts of time and money on skincare but I still use a cleanser that you can buy at CVS (CeraVe). Again, just start simple and build as you see fit.
You may suspect by the length of this post that I like talking about makeup so if you have any questions or whatever I'm always happy to add my two cents.
ETA: You're going to think I'm insane but I actually use Monistat Soothing Care Chafing Relief Powder-Gel as a makeup primer during much of the year. It is affordable and works fabulously for me except in summer, when the heat and humidity require something more hardcore.
