Hi,
I never tried to use COSMO with TPA, but here are some comments:
1. For "solvent choice", the most crucial parameter is epsilon (dielectric constant). The default is infinity, which is fine for water. For weak dielectrics you may want to check the effect of this (see chapter 19.2. in the manual)
2. For excited state calculations, the solvent response can be divided in so-called slow and fast terms (manual Chapter 19.2.3). You may want to check how your results look like if you just use COSMO for the ground state calculation (ridft) and take it out for escf. In any case, the output should give you more details on the use of COSMO, please check the output from escf.
Best,
Antti