Our pets have special places in our homes and hearts
We need to learn all we can about him - particular needs, food and housing so that he'll be cared for in the appropriate manner. Even a small monkey needs a lot of space; choose from the wide range of monkey cages online. It must be a place which is well-ventilated as well as being warm. If the space is indoors, he'll require natural light for skeletal growth - and natural light can be supplemented with full-spectrum light fixtures if necessary. If outdoors, half of his enclosure needs to be shaded at all times.
Ideally, you'd duplicate his natural environment as much as possible otherwise you may have a depressed little animal with psychological problems on your hands. And the only way to do that is to research, research and research again. Few veterinarians specialize in monkeys so, at the end of the day, it's up to you. Monkey cages are expensive, ranging from about $250 for a small, indoor cage, up to $6000 for an outdoor enclosure. You might consider building your own, but build it larger than you think he'll need, keeping in mind that he's going to grow.
And speaking of growing, you'll probably be getting him very early in his life - just hours or a couple of days after birth - unnatural as most babies stay with their mothers. Your choice of monkey cages is therefore even more important because he is being deprived of those necessities provided by his mom. Consider getting two monkeys so that they'll be companions for each other - but your choice of monkey cages for two would be even more important.
He'll need a cozy place in his cage in which to hide - plus a variety of toys. He'll need to climb, swing, rest, sleep and eat. Monkeys are very active, social animals who spend a lot of time playing. His toys should be made of wood as plastic ones won't last long with those sharp little teeth. He might like a toy tire hanging from a rope for swinging. Check outdoor play houses for children - swings and slides which are made from heavy gauge plastic with rounded edges. Plastic dumbbells, a hollowed out plastic log for him to hide in and play. Hang some pieces of garden hose in your monkey cages for him to swing on - but make sure they're well fastened outside the cage or he'll figure out a way to tear them off.
What about diet? Commercially produced monkey food is good but he also needs fruits and vegetables. Bananas of course, but seeds, berries and nuts are also important. Grubs, grasshoppers, worms - these are things he would eat in the wild and boiled eggs add protein to his diet too. Go online to see what foods and treats are available. And one last thing - you will need a veterinarian who specializes in monkeys for his annual vaccines for both his and your protection.