witch to choose witch to choose? :S need help deciding :3

[GarettM]

Ello im codding a CMS called MojoCMS from Mojo jojo ;D

lol anyways i cant decide on a few things so i was hopping i could get ur help

1) base path to cms
option a

Define('BASE_PATH', pathinfo(__FILE__, PATHINFO_DIRNAME));

option b

Define('BASE_PATH', realpath(dirname(__FILE__)));

witch on would be better to use? Ik both work and i think both are supported with php versions 4+

2) functions

so far i have been using public static function randum_function() {}
should i just use public function or can i use public static function .... ?

3) Mysql

Ik alot of people want to have cms use PDO or mysqli but alot of users know mysql commands more then anything so should i code my mysql classes with mysql commands : mysql_connect, mysql_query so users could edit or make custom code with ease?

4) Installer

Should a installer be used? or should i just make a configuration file/s and don't support noobs ??