To start, the heaters problem will be the Thermostat not a big or expensive job, get someone to check the heater pipes within the Engine bay to see if the are hot, also I should have asked sooner, have you water in the system? The Sloshing sound could be water trapped in the Bulkhead due to the water trapped blocked with leaves, If you look under the bonnet in the direction of the passenger side & below the windscreen there is a recess (Well) have a look to see if that is clear of leaves, The oil, When did the car haver it's last service? This wants to be done first including the filters (ALL) Get the system flushed out with flushing oil, the reason if that car has not had regular servicing there will be a lot of sludge within the iol ways, You say It drinks oil! How much in a month? If the car blue smokes on a regular basis Get rid of it, the piston rings are worn ( Very Costly Job).