DID VALVE REPAIR CAUSE MORE PROBLEMS- 94 Tercel

L4 1.5L 1456CC- 132,000 MILES
mechanic recently "replaced exhaust valves" entailed: machine head; oil change; replace cat convert; head gasket set; air filter; timing belt; spark plugs; timing cover gasket; dist rotor; dist cap; spark plug wires; oxygen sensor; cat cat converter; ant coolant; oil filter/oil. I have had back for about 1000 miles; about 2 weeks; in this time I have had to add TEN quarts of oil; and other day stop and go I began to run at high temp almost in red; added "stop leak" for radiator as I noticed fluid on inner rim but none under vehicle; since then the smoke billows out during stops; engine temp is little high; and although no fluid under vehicle and radiator and overflow tank were full; I checked after about 200 miles of adding stop leak and fluid spewed throughout engine; even though temps not hitting red when stopped it begins to billow out from hood; I have to add oil everyday; and notice alot of smoke from exhaust while driving; specifically between shifts. I cannot afford anymore work; and although I needed the engine work I never had radiator issue until now. Additionally even though I was using alot of oil before the work; I never used as much as the car needs now; and the car didn't smoke like it is now, I can tell you one of the plugs was not firing; he said it was running on 3 cyl instead of 4; the only plus side is I went from 17 mpg of gas to 37 mpg. Is there a simple fix for the issue I am now having; mechanic not yet informed of most recent radiator issue; but now saying that the extreme smoke may be pistons; additional 1400$ work, also not alot of oil under car; but there is a small leak in oil pan; however that was there before the repair; and once again the car did not take as much oil nor coolant as it is requiring since the repair. Any suggestions. No money left :(. IS this something that could have been caused by my most recent repair? Is there a cheaper fix. Im desperate.
also have read alot about the STOP LEAK clogging radiator etc. If this is true is there anything I can do to reverse it already being added.