Is it safe to run a propane appliance from a portable propane cylinder?
Regardless, put the tank outside.  

Plumb the house like you would for a huge tank, just bring it to an appropriate enclosure. Put your swappable tank there.  

Gas pressure is determined by the temperature of the fuel in the tank, mainly the liquid fuel since it has almost all the mass.   

Large or small tank makes no difference.

Piece of bad news though. Ever hear of the latent heat of vaporization?  1 BTU is the energy needed to raise a pound of water 1 degree F.  140 BTU will raise it from 72F to 212F (boiling). But you need to put in about 1000 more BTU to get it to turn into steam at 212F.  Only then, additional BTU will increase the steam temp further.  Same with propane. 

The problem with a propane tank is when you draw off gaseous propane, liquid propane boils to replace the vapor pressure.  That boiling propane needs to get its latent heat of vaporization from somewhere.  It steals it from the other propane, making it colder.  Colder propane has a lower vapor pressure!

Hopefully the tank will absorb enough heat from the environment to keep your propane warm enough to give usable vapor pressure.  Otherwise pressure will fade.  

Larger tank helps, as it has more surface area.