I personally prefer not to have the cells split in two.
Based on my experience, aspect ratio is not crucial in RANS simulations (of course, with some limits, even though I cannot imagine a good mesh in the outer region that has a maximum aspect ratio of 10.000 in the BL, for example). In the case of LES, there is something wrong if Fluent meshing performs the mentioned splitting (the initial mesh should have a maximum aspect ratio less than 10 and the correction should not be done).
In regards to the height of the first boundary layer, it depends on your application. The ideal situation is to have wall y+<1, although values between 1 and 10 are good for RANS simulations when no transitions model is used. In order to compute the height in dimensional variables, just type "y plus calculation" on the Internet and you will find some online calculators for your specific case.