If you know how to grow that account further and make the most of it, go ahead and make the purchase.
Or else if you're just starting, I would suggest to read the Instagram section and understand how things work.
Go through the Instragram journeys a lot of users have successfully experienced and shared in the Journey section and then when you're satisfied, start with buying a smaller account and grow it bigger. Now, that you're a pro at growing accounts, you can start buying any number of big accounts you feel are worth the price.