Hi Guys

I have a massive problem and not too sure what it is...

OK...I serviced my Fiesta last month but emptied a whole 5ltr bottle of oil in after an oil change, it says to put in 4.2 ltrs so i've obviously over filled it, I was driving down the road (at some speed) and heard a loud bang, car slowed down and a huge cloud of smoke hurled out the back (blue) which is oil, I took my car straight to my friends garage so we emptied the oil to the correct level.
My car has swallowed 4ltrs of oil in 2 weeks, I have no oil patches on the floor so it's not leaking. What could the problem be?
Heres my diagnostics.
Only kicks out a white/blue cloud when you first start the car, no smoke while on tick over, blue smoke when i put my foot down but not when driving normally.
It has only been like this since i over filled it with oil.
I was driving home the other day and my engine semi-seized up, brake pedal fell to the floor (due to engine not powering servo) and had no drive for 2 seconds, the car juddered for a sec and carried on as normal, got it home and checked oil, was bone dry, smoke coming out of oil fill cap, not even a blob on the dipstick, since then topped it up and will now keep checking every day. Car seems to be running ok and is firing on all 4 but im sure ive done some internal damage and would like a push in the right direction to see what it is, saves stripping the engine down when i aint got a clue lol

have i done damage to my pistons, piston rings, stem seals?

Please help me guys, car needs work doing but i dont know where to start, engine rebuild kit is £715 which includes bearings, gaskets, valves, head bolts, pistons, rings etc...or can anyone point me in the right direction of a cheap engine for sale?