Lighter?.......
It depends on how you look at it and what you buy in the overall Sony E-mount (A) system.
It can be a light system when paired up with lenses like the 35mm f2.8 and 55mm f1.8 or even the f4 zoom's.
But as soon as you start looking at f2.8 zoom's they are just as big as the DSLR equivalents as you can't defy the law of physics.
Smaller?....
Yes the A7 series bodies are relatively small Vs. DSLR's which contain a similar/same level of spec.
Money saver?.....
Doubtful unless your giving up a lot of DSLR kit to pay for it, bear in mind that prices go up 1st of Aug so best act fast.
Only you can decide if it's worth the money moving to Sony, try and test out the Sony body & lenses are ergonomics is a personal thing and you may not like it coming from a bigger DSLR.
Similar quality of images?......
I'd say yes, Sony sensors aren't too bad and should perform as good, if not better than a Canon's.
Lenses also play a big part in the overall IQ too so you need to decide on what focal lengths you need and then buy accordingly.
The Sony 55mm f1.8 is a great lens for the money.