Yes, you can include any number of private keys because there is no upper limit, but the waiting time will be longer.
The capabilities of your computer determine the time and number of pvt keys, overloading causes crash/shut down compulsively.
Example This user has imported more than 13000 pvt keys https://bitcointalksearch.org/topic/m.15171900
Topic: electrum - max allowed priv keys per instance (Read 161 times)
cryptosec is correct, programatically there is no limitation on how many addresses (private keys) or transactions you can have in your wallet. but practically you are limited because creating a huge wallet file, reading it, contacting servers and downloading the history (list of transactions) is a lengthy process and if you have a lot of them you wallet file size can grow huge and that makes it slower and slower until it will be impossible to use.
I don't think there's a sort of limit of how many wallets/addresses you can open/import on Electrum. It probably just depends on how much electrum program instances your device can handle.
I don't know what you're intention is with having a thousand wallets though.
EDIT: typo
I don't know what you're intention is with having a thousand wallets though.
EDIT: typo
I am importing data pulled from my laptops into Electrum and am wondering... what is the max allowed limitations on imports of priv keys per wallet instance? ... i have a really 
amount.... so if the limitations are 1k thats going to be an issue as there is history and i keep crashing the platform. IF there is another client which accepts more please advise...
amount.... so if the limitations are 1k thats going to be an issue as there is history and i keep crashing the platform. IF there is another client which accepts more please advise... Jump to: