Hi,
Addding external ram is possible with spi on 877. but not the program mem of the chip. try to use the newer 16f91x series, it is half the price for the same features.Data ofcourse can be exchanged. There are alternatives for the include files, like custom versions with only the required features, this brings down the program mem requirments. see if you require all the include files
hi
using pic16 series was also a great headache for me. then i shifted to pic18 series having same min mapping and functionality but 4 times more memory. so i will sugesst u to also shift for pic18 series