All good comments upthread. Thank you to
@secondcor521 for the essential safety cautions and the good questions about where to look for leaks when doing the sealing.
To the OP - yes, make sure you feel confident making your way around the attic by going between solid wood pieces. Please do not try to walk on the ceiling layer, because yes, you will go through. If you're not feeling good about making your way around that way, it might be a good idea to get a friend to help or call a pro, since your husband has already said he's not going in there.
As to the price difference, having it done professionally would have cost me over $3k. Materials and rental for DIY were maybe $400-$500, and we used a LOT of insulation because our attic only had several inches' worth to start. The quote I got was crazy high because the company wanted to remove all the old insulation first before putting in new insulation. I just gave them my best "do you think I'm stupid" look and said no thanks.
As to finding spots for leaks, here's what we did. We looked at where walls meet ceiling, and where there are penetrations due to lighting fixtures etc, especially those "can" fixtures, which tend to be leaky if they're not installed properly. Then we looked in the attic in those places. Additional places are where there are wires or anything else coming through that you wouldn't have noticed from below the attic. We did find one leak by the color of the existing insulation, but that was because the existing insulation was only a few inches thick. If it's more than a few inches thick, then no, you may not be able to find the leaks due to discolored insulation. Keeping track of where the ceiling penetrations are (walls, lights, fans, etc. as mentioned above) is the best way to find them.
As for baffles or vents, there were already vents installed in our attic and we just made sure not to fill them up. We didn't install any additional baffles, but they just didn't seem to be needed. Your situation may vary.
The cellulose insulation would spray around 3-4 feet beyond where the hose reached.
I didn't have a jumpsuit, but I wore long sleeves, long pants and gloves. In hindsight, a hair net would have been nice! I was at the hopper, and did not use ear protection although it was loud. It was only used for a few hours so I didn't see the need. We did have the hopper outside, and yes, it makes a mess. Please put it outside. Not inside. I think I peeled my clothes off afterward and threw them away. I might have washed them. I don't remember. I might have hosed them off on the porch outside, let them dry, and then washed them. It's best to wear clothes you can sacrifice.
Good luck whatever decision you make, OP!