On linux loksh is the package you want. It's a port of openbsd's ksh.

kshrc

On startup ksh reads $HOME/.profile. In that file you can set:
export ENV=$HOME/.kshrc

This will cause ksh to read your kshrc file. I also keep my PATH variable in .profile

PS1

export PS1='\W ' or any other of the escape codes listed in the man page. The lower case \w does another similar version to the tilde prompt.

vi mode

set -o vi