Hello 
We are currently developing a solution where our Content Team will be able to see a live preview of the changes done through Dato CMS, instead of building the website each time.
This is time by utilizing react-datocms package the useQuerySubscription() hook. We were wondering whether our current Plan would have sufficient Rate Limits or we would need to adjust our plan accordingly due to the increased load. We have team of about 2-3 Content Editors working actively
Best Regards 
For the usage you described, this should be totally fine. With 2 to 3 editors actively using useQuerySubscription() for live preview, I would not expect you to need a plan change just because of the Real Time Updates API.
The main technical cap is 500 concurrent connections per project, and the feature is not billed separately. Under the hood it uses the Content Delivery API, so the extra load depends mostly on how often content changes, not simply on how many editors are connected. The docs explain that here: https://www.datocms.com/docs/real-time-updates-api/rate-limiting. That same page also notes that when clients are connected to the same GraphQL query, with the same token, environment, and draft or published mode, the resulting CDA usage stays relatively low. The example even shows 500 concurrent users on the same query, with updates every 30 seconds, resulting in only about 4 to 20 CDA calls per minute.
So for a small editorial team, this is usually very manageable. The main thing worth watching is only whether the project is already close to its monthly CDA quota, or whether the preview opens lots of different subscription queries at once. To keep usage even lower, a very common setup is enabling real time updates only in Draft Mode for editors, which is also the pattern shown here: https://www.datocms.com/docs/next-js/real-time-updates.