91 caravan troubles

just got a 91 caravan it has some problems.the engen light keeps cooming on but gos right out if you restart it. I dont think the fan ever comes on. It has a temp. gage that works and it never gets hot. Im thinking the two are conected (engen light and fan).C.V joints are shot but I can handel that.Air bag light is on, hopeing its just the sensore. And it leaks oil,comeing from the right side of the motor.Ive been told vavle covers. If its the front main seal how hard is this to fix? And how much gas dose the gas tank hold? I dont think Im getting very good gas mileage.Its a 3 liter auto.And it smokes just a littel if its been sitting over nite but gos right away when you start it. ive put a cap and rotor on on it and that seemed to help runs a litttel smoother, uses less gas. looked at the pulgs and they werent oil fouled but had some deposets-witeish.they will get changed next.Any adviec would be great thanks!