I'm sure we saw permits lodged for both a North and South Paintshop, that is not totally conclusive, but for now I am assuming they are adding a new Paintshop.
There's strong evidence for "South Paint" being constructed from the various Fremont permits cited by
@kengchang. Time frame of completion is unclear, but the baseline would be that Tesla timed all expansion projects to complete in a specific order to support smooth Model Y ramp-up. I presume first Model Y's are using North Paint.
This is their third paint shop, so ramp up should be swift.
I think the 35GWh production of cells in GF1 limits them to a combined 10K per week Model 3+Y, until they do something to add pack capacity.
There's two unconfirmed leaks/reports that Tesla aims for 15k packs/week at GF1 and Panasonic can now do 50 GWh/year (!), which with (80+53)/2 = 66 kWh average pack size and 95% pass rate of Panasonic cells defines a ceiling of around 13,800 packs/week in 2020.
Limit is probably pack assembly speed at GF1, which is currently at around 10k/week SR packs, fewer LR packs. I presume it's being ramped, plus GF3 pack assembly is ramping to free up GF1 capacity.
I'm inclined to believe battery investor day will reveal that something...
I'm 90% confident that the Maxwell technologies need scaling, I.e. a new factory. Probably not used in GF1 yet.
I have no clue on stamping or the capacity of the body lines themselves...
There's a new Model Y body line at Fremont, with stated capacity of 2k/week by the summer. Design ceiling unclear, but I'd assume at least 5k/week.
Keep in mind Tesla thinks Model Y can do 2X Model 3 worldwide, and that Model 3 volumes will not drop..
So Fremont being limited to 10K Model 3+Y per week is possible if China ramps rapidly....
But I also think 14-15K per week Model 3+Y may be possible if stamping supports it...
Fremont stamp was stated to support "8k/week, up to 10k/week with low capex" Model 3 capacity back in September 2018, by an independent audit.
Stamping capacity ought to be freely allocated between 3 and Y, as die sets can be changed and stamping can be batched. New Model Y cast parts (I presume made at Lathrop) might reduce stamping load.
Paint shop capacity is elastic between the 3 and Y as well, and so is seat factory and most subassemblies. I think some cannibalization of Model 3 by Model Y is possible - otherwise Tesla would not have hidden their Model Y plans so well. It doesn't really matter as long as most Fremont capacity and battery supply is maxed out.
Fremont assembly line worker crews can be load-balanced between the Model 3 and Model Y lines, so they can max out the workforce as well.
10k/week out of Fremont ought to be possible with the Model 3+Y, 15k/week total with Shanghai Model 3, 20k/week with Shanghai Model Y, but 2020 China cell supply is rumored to be 10 GWh/year, which supports GF3 3k/week, maybe 5k/week with GF1 help.
I'd be happy with Fremont+GF1 scaling to 10k/week and Shanghai to 5k/week by the end of this year, which gives a global EoY 3+Y run rate of ~780k/year plus S/X - 850k/year.
2020 deliveries and production, assuming a linear scaling from 430k to 850k would be around 640k - but official guidance could be more conservative at 520k-560k, at least +40% growth over 2019 deliveries. I'm not sure what 2020 and beyond growth guidance big investors are expecting Tesla mgmt to make.
Excess GF1 capacity might be used for China, the Semi and Powewalls/Powerpacks/Megapacks.
As usual, I'll likely be wrong on some of this, and there's always headwinds and complications - so this is not advice.