"I am contemplating going with an 8 instead of 4 so i can use 1 FXO and 7 analog phones or maybe 2 FXOs and 6 phones."
You had better know exactly what you need now, and what your maximum capacity in the future or you going to waste money.
The TDM400 accepts 4 single modules of either FXO (analog telephone lines POTS) or FXS (terminate an analog telephone), for a total of 4.
The TDM800 will accept only 2 modules, either single or quad modules. (which means 2 singles, 1 single 1 quad, or 2 quads
In your case, that means having a single FXO and a quad FXS to 4 single line phones, which isn't what you want. A second pci card would be needed.
You may want to add IP phones instead.
On my system, I have the TDM400 with single FXO, 3 FXS and 3 aastra 9133i phones