I can give you no tips for plastic mesh, never worked with it. But I guess the people who make suits could give you tips. Maybe  joecifur or  mushimagicsuits for example.

I would simply build it from styrofoam instead, easy to cut, easy to glue and lightweight. Simply use the measures of your head for gluing together a strofoam box (from those styrofoam plates you get pretty much everywhere, the styrofoam pieces in packages for any electronics and household items also do well when cut in shape) cut off the upper edges, and glue plates over them to get it round and covered, glue on a smaller box for the muzzle and more plates for the parts that will be wider than your head, and then simply carve your Raichu head from it.

Though you need a styrofoam cutter or a sharp knife to cut it, sawing it gets static sawdust everywhwere. Better a cutter.
Drilling many little holes trough the foam and only covering them with the fur layer itself helps keeping it cool.
If you think it could break to easily, styrofoam is also easy to reinforce, simply force a pointed piece of wood into he foam into the planned direction.