As indicated by narx's answer to a similar question on ELU (English Language & Usage, ELL's "sister site" aimed primarily at linguists, etymologists, and serious English language enthusiasts), only little can be used as an unqualified noun to mean a small amount (where adjectival small needs an explicit noun, such as amount or quantity).
The other interesting point made about little there is that in...
1: I have a little experience teaching English.
2: I have little experience teaching English.
...the two sentences have almost opposite meanings - #1 implies you have at least some experience, whereas #2 implies very little (perhaps almost none). In fact, #1 is often used somewhat facetiously to imply you actually have a lot of whatever is being spoken of.
Apart from the above distinctions, there's also (as kiamlaluno points out) the fact that little often carries more "affectionate" connotations than small. And from BBC Learning English, little is more common in the sense not much when coupled with abstract nouns such as hope, chance, change, effect, use and point.
In most other contexts, there's little to choose between the two words. Use whichever you like.
I cannot speak to English elsewhere, but in the US there would be no need to use size at all—‘small business’ is the term.
If you are concerned that bare small suggests inferiority, quite the opposite is true. ‘Small businesses’ are generally recognized—or at least recognize themselves!—as the engine which drives the American economy, and there is a large Federal agency, the Small Business Administration, dedicated to their support. They have indeed something of a mystique: ‘small business owners’ regard themselves as a distinct class, superior in efficiency, energy and entrepreneurship to the bureaucratic managers of large corporations.
Of course the US notion of ‘small business’ may be substantially larger than that which obtains in your country. The SBA standard varies from industry to industry, but by and large it is less than 500 employees in manufacturing and less than $7M annual revenue in non-manufacturing industries.
Best Answer
This question is related.
Elaborating (though I don't think that any more needs to be said), both small and little are fine to say.
The sentence is not using small or little as quantifiers, but rather to denote the size.
However, it is perhaps worth noting that little question is more popular.