For knife mode only You may need to load csdm.cfg with such settings for [[equip]] section:
[equip]
menus =
autoitems =
grenades =
All of them are empty - so no menu and no equipement is loaded, but start weapon are stripped out - the players should have only knives. Read more in some sticky here how to load map specyfic config (if You want it so only for some maps).
About grenade arena - take this plugin , install it and write in console (while playing):
amx_hearena
and You will have what You want.
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