To sum up (I think):
We will continue to call them 'nanpa suli' regardless of suspicions about the literal correctness of the expression (but most idioms -- indeed compound expressions -- are not literally correct, else they would be a lot longer).
For the main remaining use of numerals, it would be nice to have a set of proper adjectives for reading them (the letters, too). I would say, just read them in your own language except that we are not any longer mutually intelligible, so make them up out of some simple stock or a priori.
The basic ideas of the tp numbers are unity (wholeness, integrity), divisibility (separateness), and frisibility (shattered, crumbled, spread about). If 'nanpa wan' can refer to the number one, and 'nanpa tu' to two, then 'nanpa mute' can refer to any number for than two. But all of these expressions, while legitimate, are ill-advised since they give rise to more likely readings in all but very special contexts. In any case, 'nanpa x' is probably not a good way to quantify a noun phrase, since it would clearly have an ordinal meaning before it had a cardinal one (in non-specialized contexts). (Also, it seems to require 'pi' for the cardinal use, while ordinary cardinals are automatically right grouping. Ah, but 'nanpa x' as an ordinal is also automatically right grouping, so there is a disambiguator.)
All of this last is largely irrelevant since tp is designed to wean away from all those big numbers to things we can really deal with and regular ways top deal with them.