1. Would it be feasible for me to do this myself or should I get a pro?
2. Is it OK if I put unfaced rolls on top of the existing loose fill? Or should I put more loose fill on? Or do something else?
3. If I do unfaced rolls, does anyone have any recommendations on types, brands, or where to buy for the best price? If I have to do loose fill, do I have to lug the spraying machine into the attic or can is the hose long enough to spray all over?
4. Do I need to buy those plastic things that prevent the soffit vents from being covered up or is that unnecessary?

Thanks!

You should buy those plastic things but you could just skip the last 12 inches or so - not ideal.

any duct sealing should also be done prior to insulation
install.
plenum to equipment connection, duct takeoff at plenum
and supply boxes to attic floor.
return caulked.

best of luck

There are several Youtube videos showing blown in insulation installation. It is a messy job, but doable for the DIYer.

I'd go batts over cellulose anyday. not everyone
agrees, but the fine particles from cellulose
finds its way into your living space via
cracks between attic and living space.

you should invest in the air sealing first.
and duct sealing if your ducts are in the attic.
lots of humdity issues in our area.
you don't want to filter hot humid attic
air thru the insulation and into your home.
caulk and mastics are easy to work with.

best of luck