Question regarding Ionic 4

Can i start using Ionic V4 for application development in my company?

Depends on if you company is ok with beta software being used for development.

But what are problems I am going to face if I use beta version.

No idea.
You might find bugs, that are not known yet.
Stuff might change until the final release, so you will have to update your code.

Yesterday beta.1 was release, so you can see what bugs were fixed from beta.0 to beta.1: