1) Pry it out gently and restrain it as you do so. After a time or two you'll get the hang of it.
2) Very thoroughly when the gun is unboxed the first time, to get the preservative out of it. Lube lightly at that point. If you keep the gun dry and out of the dust, and keep your ammo clean, the gun can go for years with no further attention to the magazine tube's insides. If you get it wet/dirty/dusty/drag it through the mud, then clean it. No need to obsess over it.
3) See 2) above. Same thing goes, pretty much. But resist the urge to take the trigger plate apart- there are no user serviceable parts inside. If it needs cleaning, use the spray/soak/blowout method and clean it as an assembly. Under normal conditions it won't need a lot of attention. It's not delicate or anything- it's a pumpgun after all. I've pulled trigger plates out of bird hunter's 870s and had enough weed fluff etc fall out for a bird's nest.
Try to wear it out by SHOOTING it, not cleaning it...
lpl