Bass tackle injectors are the easiest to use with the quick disconnect nozzles. Baitjunkies plastisol is the overall value pick. I would check the classifieds and Ebay for injection molds. You can pick up some good deals there.
You can try a local boat repair shop also. Most may trade some for a few bags of baits. You can also get some unique colors and they tend to have larger sizes than regular body shops.
Check with your plastisol supplier and ask them to sell you some MSO. MSO is essentially worm oil only cheaper because it's not called worm oil. ( and no scent or glitter.)
I use the IR just for the quick reading of the plastic. It's real handy when shooting laminates so as to keep both colors close to the same temperature.
Frank has a YouTube video where he uses the griddle to keep the plastisol at a usable temp. You can also get a meat grinder from harbor freight and grind the sprue, it will heat with less time, and the heat stabilizer is a must.
Cross contamination won' be a problem. I pour in my garage and have all my toys stored there. Just a small work area to store some plastic, coloring. scent. Molds and heating equipment is all you need. Your idea for ventilation should be sufficient for your production. Just keep reading and asking questions, there is a wealth of information here.