Embarking into breeding a mare is a daunting prospect. But if it is something you want to try, it will be an experience for you. There is no way someone on the internet can say whether it will be successful for you, or whether it is a good idea to try this. Many people have, and the results are always somewhere on the scale, from disaster to success. But a learning experience, for sure. Caution, breeding horses can be addictive.
With a first time breeding owner, I would suggest finding an experienced mare, not a maiden. Maidens can be fine, and have other advantages, but when it comes to producing a foal, it is nice to have a mare who has been down the road before. Especially if you haven’t.
The registry thing is not important to me, it is important to others. You have to decide how you feel about that. Get a nice mare, who speaks to you, who is reproductively sound, who has successfully raised foals that you like, with good milk and good mothering skills. Then explore your theories on what might make a good cross for her. No horse is perfect, but some are pretty close to “perfect for you”. No theories are right or wrong 100 % of the time. Do some reading, talk to others, and make your own decisions. Your horses pay the price of your decisions, as they always do. All you can do is do your best.
Good luck, and try to enjoy the process.
If you are looking for a TB mare, sometimes a good place to look is at the TB sales in the fall. Broodmares who have currently unfashionable pedigrees, or who have not produced stakes horses already, are often cheap to buy and repurpose as sport producing mares. They are already in foal, with the stud fee paid. You get a TB foal in the ground within a few months, which you can either raise for your on purposes, or sell. Then can breed the mare back to the stallion of your choice with some idea of what she produces and how well she mothers. If you get lucky and her previous offspring suddenly wake up on the racetrack, the free TB foal can suddenly get valuable when offered for sale back to the racetrack owners. Then suddenly, you are the breeder of a racehorse and can gain breeder’s bonuses in your area. Best case scenario.