can this be connected to a variable fan speed controller?

I've got an array of 3 of these connected to a variable speed controller (which I think is of high quality... $20 on amazon). It works great. Fan is much quieter around middle speed, it becomes almost silent. Back to full speed with max airflow is needed. My rule of thumb is to dial the speed up to where there is no hum coming from the electric motors (I suspect this sound isn't a good thing, so I dial up speed until it goes away).

is this fan can be conect to a duct to blow air out of the house?

I put it on a basement window. A duct boost fan is probably better for what you need. They are also metal, this is all plastic and not that strong,. At 170 CFM, it’s ok. They have 6 inch duct fans that are 240 CFM rated.

I can't find an installation guide for ceiling. Can anyone send it to me?

About the installation 1.Wall-Mounted Installation A.Install it with glass glue a.Dig a hole in the wall b.Insert the exhaust fan into the hole,fix it with glass glue B.Install it with screws a.Loosen the product panel's screws to disassemble it. b.Try to insert the base of exhaust fan into the hole,and make the screw position mark c.Bore a hole in the position marked and stuffed plastic stopper d.Insert the base of th exhaust fan into the hole and and lock the screws e.cover the panel,install completed. 2.Glass Window-Mounted Installation a.Dig a hole in the glass window b.Insert the rubber ring into the edge of the glass c.Insert the exhaust fan into the hole,fix it with glass glue 3.Ceiling-Mounted Installation a.If the ceiling is thin aluminum buckle or gypsum board,unable to bear the weight of the product, It is recommended to fix it by increasing the plank,suggested plank size is 20*30cm. b.Dig a hole in the ceiling c.To install the exhaust fan in the ceiling with the methods B installation with screws. d.To connect the bottom of the product to the ducting with the duct clamps,cover the panel,install completed 4.Tips a.Applicable drilling size is 150mm-200mm,recommended size is 155mm, the recommended size of the hole in the glass is 150mm. b.If the ventilation fan is ceiling-mounted,air supply distance should be controlled within 2 meters, Not recommended for using this product over 2 meters c.Include the rubber ring and the screws. Best Regards, Hon&Guan