If you have the budget for it, we recommend you start with two hives. If not, then one is just fine. But with two hives, you will be able to compare the two. Is one doing better than the other? Maybe one hive has sick bees and your bees are telling you something? Or one hive has calmer bees than the other? One hive produced more honey than the other.? Those are good questions and observations to share with your mentor or fellow beekeepers.
With more than one hive, you will have more management options than you would if you just had one hive. If a hive becomes weak, you can transfer a frame of brood, honey or pollen from the stronger hive to the weaker one. Or if you happen to smash the queen by accident, you can take a frame of brood from the other hive and the bees will rear their own new queen. Yes, even highly experienced beekeepers occasionally smash queens when removing a frame and we all feel terrible about it.
Many things can go wrong through no fault of our own. It’s just the nature of beekeeping. The learning curve is steep for beginners. So starting with two hives, you will have a better chance of your bees surviving and you will be able to keep them healthier..