Welcome to the forum, from another newcomer.
I do not believe that keeping all your money with one fund company (for example, Vanguard) is risky.* I used to think that, but now I have all my money with one fund family, and find that there are great advantages.
Click here for an article from Vanguard on this topic.
With all your money with one fund family:
1. You can receive discounts and special treatment if you have a high balance.
2. It's easy to move money from one fund to another
3. Your record keeping is simplified and consistent
4. You can see how much you have on a single web page.