Welcome welcome!
Three things I can suggest starting off as a new grower that will help you tremendously. And for a while it will probably feel liike there is always some extra thing to buy. However, a lot of it lasts a long time and will be used in future grows.
1) A pH meter/pen. The proper pH of your water and any nutrient solutions you mix up is essential to success.
Top companies:
BlueLab
Apera
I personally use a Milwaukee Instruments pH600AQ as it's ~$20 and has a calibration adjustment. I don't know how reliable the $10 cheap amazon/china/ebay units are.
You will also need calibration fluid and storage fluid so budget a bit for those. Relatively cheap but around $50-60 for the whole kit.
2) An EC/PPM meter. Knowing the "strength" of your starting water and any solutions you mix is key to maintaining your plants.
Shop around as you like. I have an HM Digital COM-80 myself. No cal or storage solution needed. (I do have calibration fluid)
It is inconvenient having separate pH and PPM pens but I found an all in one unit to be cost prohibitive especially just starting out.
3) A pH adjustment kit. Several available out there. The General Hydroponics pH Control kit is $20-ish and comes with a bottle of pH UP and DOWN, plus a small pipette. This stuff is highly concentrated, dangerous, strong, but works well. So just be careful and use a little, very little, at a time.
If you've got all that sorted out you'll be making tomato sauce in no time!