TL;dr -- it's most economical to operate nuclear plants at a fixed output level, so other fuels are used to adjust for variations in demand. Nuclear output at any given time is limited by outages, which are driven by the need for refueling and routine maintenance.
Nuclear plants aren't load following, so other sources are needed
From Wikipedia's article on ...
Change in capacity
From 2004 to 2014, nuclear capacity did not change substantially:
Change in generation
However, the generation mix did change quite a bit (2014 nuclear data not available, so this chart ends in 2013):
Summary of data
Here's a summary of the data from 2011, along with the two years before and after:
Your figures are a bit out, but broadly in the right area. Using observed figures for the numbers you've estimated, I get 1,246 km²
90% capacity factor for nuclear is probably optimistic, but some jurisdictions have achieved it. The global average in 2018 was 81%, but that's an overestimate, due to the way that reactors on long-term shutdown are handled.
Current high-end windturbines (WT) produce about 4.5 MW while being about 240 m high (top of rotor tip) and with a rotor diameter of 150 m.
When it comes to the distance between the WT, rule of thumb says 5 times rotor diameter in main wind direction, 3 times orthogonally, leaving us with 750 * 450 m per WT, which is about 0.33 km². So you can (if you place ...