This is from an Art Professor, professional artist, and juror of decades of experience:

First, you are correct to get good color, exposure, and sharpness in perfectly justified (rectangular) borders.

Yes, you can get very expensive and very professional. You do not need to, if you learn a few things about post processing. If you are doing a few, even Mac Photos will suffice. If you are going pro, I would suggest Photoshop or an equivalent.

Set up your lights as illustrated. You can even use floodlights in clip on pans, so you can avoid stands or tripods at first. BALANCE them. Same voltage and age. Make sure the outside of each light is near the near edge of the painting (arrows in illustration). Place a white surface (white paint on a piece of paper, for example) in the shot, to be cropped out after adjusting white balance.

Adjust white balance. There are SO many ways. If befuddled, google "correct white balance in [name of your program]." If you are going to be going pro, I strongly suggest Photoshop or its equivalent.

If struggling, ask someone, here or another artist/photographer.

I use these techniques on works seen on my site, robertstanleyart.com. As you can see on my resume, I have works in museums, so the techniques work. You may want to upgrade to some of the suggestions the calibrates have suggested. They work, but.....not necessary if you know how to light evenly and post process. Once I had a pro shoot some of my works. Turned out great. Looked the same as the ones I shot and processed the way I've suggested, without the sweat, time, and money spent.

Work at it, and you will be fine.