Just a suggestion. Give up on the flow hood idea from a used air filter totally. Flowhoods, schmuv boxes, and filtered GBs all sound great, but how do you know what they are providing is actually sterile or a sterile environment? You dont.
If you have a heavy spore load of contams in your place, just do a still air, sealed glove box. Just a clear plastic tote with a lid, Holes cut for arms and gloves attached. Sanitized and clean. Plenty of GB plans here and you don't need anything other than sealed. no fan/filter/ hepa none of it.
Sanitize it and Only open for inserting your items. ( jars. syrs, etc.) Then sanitize again. Every time with a bleach/water solution.
Keep it simple! Unless you are working with wild or unknown prints on agar, there's no need for a flow hood, filter air movement of any type, or agar.
Don't experiment, until you've got the process down 100%. It will lead to more failure than success and pure frustration, questioning what went wrong and where this time?, again and again.
I've done all my work in a disgusting, dirty, 75+ yr old basement with leaking in ground water, mold, algae, mildew etc, using a 70 yr old pressure cooker for sterilization. I only use the glove box on a rare occasion. Or to store freshly pc'd items or jars until ready for use, and then to do the work if its grain to grain or something that exposes my grain to open air txfers.
Even Nocc'ing jars can be in open air, If you are prepared, clean and follow your procedure every single time.
You certainly dont need a hood for making syringes! Just clean, open face prints, in new mini ziplocks,(preferably for ease) and sterile water in a sterile syringe.
You don't even need a glove box for that portion. Just some 90% iso alcohol on a paper towel, and a lighter to sterilize the sharp. Straight from mini zip to syringe without ever opening the baggie. For this you should practice without real spores. 100 mini zips 2x3 at wal mrt in craft dept. $1 dollar.
I haven't read all your posts, but advise you read up on proper grain prep and pre- or soaking prep, or pftek, and proper use of a pc/ sterilization techniques. Understand its not about the amount of water or grain you use, but about the grain being hydrated properly. For everyone in every environment that will be different. Use the teks here as guidelines, but realize it may not fit your situation exactly. Most green comes from improperly sterilized or prepared grain, If it is happening in three days, next time you make jars, wait 5 days after pc'ing before you innoculate. See if they contam in that time. NO?, then you've isolated a potential problem and know to look elsewhere. I always leave one jar alone.No spores. Just to see how clean my grain prep and pc'ing were.
If your grain or pf jars dont look exactly as they should before and after pcing, you're wasting your time, money and spores.That means no excess water in jars, your cakes dont look like slurry or mush, your grain is not exploded or totally wet looking etc.
If you don't use a pc, Pftek/steaming is the only way you have a chance at success. Sure others have succeeded in other ways, but not until they got their process down, and not reliably. And especially not in an environment with heavy contam spore load.
I realize there is so much info here, and piecing together a plan is difficult. You want to try what all the experienced guys do,.so many options!. But for your situation. Lessen the probable causes of contamination, reduce the variable,,.simplicity rules, and patience prevails.
Im not trying to sound condescending I Just want you to succeed and every variable you add beyond a sterile sealed GB for work, is an added chance for failure. There are many ways to succeed. But just as many that insure failure. Lessen those chances. Simplify, stay basic, then work your way to experimenting, before you get disgusted, frustrated, and just give up. You can do this! We can help you.!
Best of luck, foster