To answer this question, first, one needs to know the basic difference between a demat and trading account. A demat account is an account which is used to keep your shares in an electronic format. A trading account is an online account which can be used to place your trades over the exchange.
In India, there is no restriction to the number of trading accounts or demat accounts that one person can hold. You can open as many trading accounts as you wish and the same is the case with demat accounts. However, you need to link every trading account with a demat account if you actually wish to use it to trade.
With Upstox, the account opening fees (Rs. 150 + Service Tax, per segment) and Demat Account maintenance fees are minimal (Demat AMC is Rs. 150+ Service Tax). It is always advised that you maintain proper records of any account that you open.
You can read more about opening a new demat & trading account in our linked article.