Enclosures can be built but need to be designed right and need more
than a few inches of airspace. The heat from the motor and exuast will
ignite wood. I use an 8x8 shed with some insulation at the roof and
leave the doors open and run a fan inside. Contacting a pro or the mnfg
is best.

Mufflers will work but will reduce power.

Sure Honda is the best but at 2.5-3x the price. But you do get what you
pay for, in voltage stability, reliability and quietness.