Your diagram looks pretty well thought out in general, you’re on the right track.
On the fusing issue, depending on the risks involved with installation/placement some would recommend a separate 10A fuse on the +5V before it goes to the 2 injection points on each strip. That way if something shorts in a strip, the fuse blows before the wires melt.
Now that you have some idea of the worst case current requirements for each strip, you can work out the potential voltage drop issues. You can use one of the drop calculator’s in the tutorial section of https://kno.wled.ge (@tonyno’s right, this a great resource), I like:Voltage Drop Calculator. Set it up for DC, 5V Plugin the max current you’ll need for one side and the actual length of wire from the PS to the injection point. I’d start with 18AWG wire and work up if necessary. This is about picking the right size wire for the distance you want to carry your needed current.
As far as data lines, you’ve drawn this up where the two strips are fed from a single data source.
Each strip will display the identical colours as sent from the MCU, if that’s all you need this will work out.
You could also split the data so you have 2 independent lines from 2 GPIO’s on the MCU. That gives you the flexibility of duplicating the colours in WLED or running things separately.
The need for a resistor will be highly dependent on the length and location of the data wires. As @tonyno mentioned, 470 Ohms is very high start at no more than 220 Ohms and work down. I personally don’t use them at all. A level shifter may or may not be needed to bring the MCU output up from 3.3V to 5V levels. The capacitor is ok, although I find them unneeded if you have good power connections.
My mention of TxRx pairs was discussed in: Personal project for my backyard... which way to choose? - #5 by divsys and Long Data Wire + ESP8266 + Level Shifter - #7 by divsys. They come into play when you have a long run and don’t want to mess with trying to force TTL data to play nice. IMO TxRx pairs are the easiest solution to long run issues.
Have fun looks like you’re well on youur way 