4 plants sucks but it's better than what we can grow now, legally. With training you can get 8-12 zips per plant outdoor and keep them under the limit so technically it's enough if all you want is your own smoke.
imo, the trick will be to just stay under the radar if you want to grow more, breed, etc. There's nothing in the legislation that I can see where you'll have to register to grow within the limit - federally. That said, I think there will be at least the odd province who may choose not to allow home grows or even municipal level governments restricting it so much it wouldn't be worthwhile. So again, keep things under the radar, don't grow outdoor, make your own seeds.
Reason I keep saying stay under the radar is what they won't be able to do unless they impose it provincially (which would be shot down by the courts at first challenge under the constitution) would be to enter/inspect your residence unannounced or at minimum without your permission. That is clear in the proposed legislation under Part 7 (Inspections), section 6 & 7. That essentially states that they cannot enter your dwelling without permission or a warrant if you refuse permission.
In addition, it would be impractical for them to have everyone register to grow (there's no indication of registration for rec legal in the legislation that I can see), whether indoor or outdoor. It would cost too much and be a cluster f*ck, just not seeing it.
So, just like many of us do now and some of us have done for many years. Continue growing, don't tell anyone other than maybe your significant other and if anything it'll be easier than it is today. With many more people growing rec + registered medical growers, law enforcement will be busy enough and have many more easy targets to bother with someone who as far as anyone else knows, doesn't even smoke pot, never mind grow it.
As far as the questions around
legal ways to obtain "starting materials" being clones or seeds. That's not looking good in the legislation. Meaning that federally as they control the sourcing which means LP's only and you can't make your own seeds. It's looking like it will be imposed/restricted to LP crap and looks like they'll be at least trying to clamp down on seed distribution. e.g. Part 1, section 13 (1) where it says: "It is prohibited to possess, produce, sell, distribute or import anything with the intention that it will be used to produce, sell or distribute illicit cannabis". The pretty well says it all