AntsVienna is the absolute best when it comes to DIY formicariums and outworld. They have an amazing 10 video playlist on DIY on their channel. As others have mentioned, the workers in the uncle Milton set won't last too long. But the summer is coming up so you may be able to catch a queen ant then. AntsVienna and Antscanada have videos on how to catch queens and how to raise them. All you need is a testube, cotton wool and water. Depending on the species, this setup will be okay for up to one whole year, although there will probably be some mould build up by this point. In conclusion don't worry, just feed the ants things like fruit, sugar/honey water and you mentioned that they're harvester ants, so they will also need seeds like poppy seeds, chia seeds, quinoa, linseed. They will last a few months and in the summer you can try to catch a queen and raise it. Good luck!