You want A New Threat- it's a fantastic overhaul that is more challenging than base game but not overly hard or frustrating.
Get the QHIMM Community Packages in 7th Heaven for Field Models, World Models, etc, Media (ie movies), etc They will all be listed in the catalog that comes with 7th Heaven.
Enable the modules then double click for options. You can toggle everything you want from there.
For visuals I would recommend "SYK" (Sasuki) upscales everywhere they are offered.
For character models go with Ninostyle when offered (this will give you he ones that look like Nomura's concept art) and Kaldarasha otherwise. That will give you the "realistically proportioned" models.
Another alternative is downloading Ninostyle's chibi field models (IRO version) from the
Nexus and then import the IRO file into 7th heaven. These chibi models are insanely good and their proportions work better with the environmental art in the field. However only about 20% of them are complete so far and he still hasn't done chibi-style models for some key characters like Cid, Vince, and Elena. I started off going with the "realistic models" but have now settled on Ninostyle Chibi (where available) and vanilla models otherwise. It's a good balance.
It's all very easy to toggle on and off with 7th heaven so just download the modules and then you can can change things around to your heart's content until you hit your personal sweetspot.