If you want to make a map for this gamemode, you should know a few details.
First, your map MUST HAVE:

• the name starting with MHK or MHM, depending on if you want Kamikaze or Marsh Hopper as monsters. For example, "MHK_Medina.wld" or "MHM_CairoCity.wld";
  
• special spawn markers. All spawn markers should look like this images.akamai.steamusercontent.com/ugc/112983518036245294/F1BEC5DEA3FE38BE3EA9805060E2ED806BDBD39B/ i.e. have 250 hp/armor and only hands weapon;
  
• special static model for human spawn. Basically, it is just an empty static model with name "HumanSpawn", located where you want human to start round images.akamai.steamusercontent.com/ugc/112983518036243721/350BAD95353B1436973E89325E897DB9C9A05D4F/
  Better switch "Controlled from script" to "Game scripting", though iirc it is not neccessary;

You don't need to place any weapons (and you shouldn't) - Human will get weapons automatically when he is chosen. Only ammo (shells and bullets) and health/armor.
If you are making a Kamikaze type map, you should make sure that the Human can't get to the higher ground and safely sit there, as Kamikazes cannot jump! Add some invisible walls or invisible ceilings to prevent that.

You can always look at the existing maps, they are located in /Content/SeriousSam3//Levels/Z5_Other/