Wsalam. Very litt;e acceleration could be due to one or more of the following reasons.
The Carb is not set right
Since Its a point based 125, a badly worn point or incorrect setted point can prevent the bike from running right
The Piston or the Ring's are worn which isn't letting the engine making enough compression
The Cam or Tappets are worn
The Clutch or/and Pressure plates or the Clutch hub is worn
The Weight or in technical terms the crankshaft or Rod is damaged.
Vibrations can be due to the Crankshaft bearings being worn or the Balancer being worn or it could be because the engine bolts are not torqued as much as it shouldb leading to the engine being shaky and making the whole bike vibrate.
Oil leaking from the front bottom could be due to the magnet seal's being worn or the oil filter bolt seal being worn or the oil could be from the oil extractor nut which is located beneath the engine. if everything else is okay then it most probably could be from the engine piece bolts not being torqued enough, could be also due to one or more bolts missing or because the mechanic didnt seal teh engine right.