I think this is a fair question. However, it does hit on a more intimate question for some founders. Here's why:
I think it is better to ask questions about the structure of the investor group rather than the amount. I would focus on asking these types of questions (I'm assuming angel investors rather than VC's because I think angel funding is easier for startups - VC's come later when you're ready to chew down $5M or more for growth):
It is extremely important to have more than one deep pocketed investor for any startup. Why? Because someone is always sideways in an investor group as the years go by. If the group only has one deep pocketed investor - and that investor goes sideways for whatever reason - the company can become seriously unstable, having to hunt around for last minute capital. This can put a company in a toilet bowl flush since the founder will be distracted hunting around for more investors instead of keeping eyes on sales and marketing.
The question on sales and marketing will really give you some insight. If the founder loves all things technical and is still early in their sales journey, you'll see a tiny sales team and a bloated product/development team. If there's a good balance of sales and marketing folks, that should give you more comfort.
In the end, any startup is filled with risk. Be comfortable with the founder's ability to continue to raise capital until break even and to sell (if he or she is raising capital then they can sell).
You can also try to get a feel for the dynamic between the founder and the investors. Does the founder complain about the investors or show respect? You can glean lots of insight if you just listen to the choice of words the founder uses when describing the investors and the kind of relationship they have together.