The only comment I have is that for a 4" system like you have your hood may be too big for your fan. I'm guessing that fan is good for 100 cfm or so? And I'm guessing your hood is about 6' x 2'? You only have about 8 ft/min face velocity. That is really low. Typically the face velocity should be a minimum of 60 ft/min.

You can try what you have and if you are happy, you are the only one that needs to be satisfied. If it were me, I'd discard that hood and use something like this.

Welding Fume Nozzle

I'm not cheer-leading for this particular one, just the concept. We used this style at one of the power plants I worked at. We had a common large blower with a suction trunk that had individual drops for each welding table using hose and a bell style end with a magnet attachment. Worked for us. In fact, if a weldor got the hose to close to the work they complained it was like welding in a windstorm!