Of course there are restrictions. Every contract is different, and so is every futures company. Generally speaking, the exchange will set an upper limit for each futures company (either absolute number or proportion), and will also set an upper limit for the position of a single customer. The purpose of this regulation is to prevent the risk of large households manipulating the market.

Of course, if you do it yourself, this restriction is basically unnecessary and sufficient.

Your question is not clear. My understanding is the number of listed contracts for a single variety. Understand this, there is still no fixed answer.

The number of listed contracts of a single variety depends on two factors, 1, the longest possible trading time of the contract, and 2, the contract month.

For example, contracts can be traded for up to one year, and there are contracts every month, so the number of contracts is 12.

The longest trading time of domestic futures is one year and one and a half years, and contracts are linked every month and every other month, so the number of listed contracts of different varieties is different, at least six, and at most 12.

The situation abroad is more complicated, and the longest transaction time of a contract is several years.