As far as I can recall you can use Sourcemod to give yourself immunity to pretty much everything by default. Personally though, while you may full and well be the server admin/owner, I think it's a dick move to kick others for going afk and not yourself, since it's kind of hypocritical , but if you need the reserved slot then just use... the reserved slot system (which I believe is also already built into Source mod). If you don't already have Sourcemod installed then you can find everything you need here
http://www.sourcemod.net/ .
You can also find any plugins you need at their site.