If I have 2,000 items, is it possible to mint all of them at the same time, or is there a limit for the number of items that I want to mint at the same time?
If we suppose that there is no mint limitation by the item owners (which is commonly implemented in NFT projects), one limitation you may encounter is the number of transaction that can be included in one Ethereum block.
To go deeper, here is an extract of this article, pretty old though:
Currently the maximum block size in Ethereum is around 1,500,000 Gas. Basic transactions or payments of ETH from one account to another (ie not a smart contract) have a complexity of 21,000 Gas so you can fit around 70 transactions into a block (1,500,000 / 21,000).