It’s always good to be cognizant of trace lengths when you’re laying out a parallel bus, though at moderate frequencies it is nothing to stress about. The propagation time for a signal traveling through a trace is maybe 150 picoseconds/inch. So if you have two traces with a length mismatch of one inch, one signal will arrive 150 ps after the other signal. If your signals are transitioning at a frequency whose corresponding period is much greater than 150 ps, this one-inch mismatch won’t cause problems. Even at 100 MHz (which is pretty fast for a parallel bus), the period is 10 ns, i.e., ~67 times larger than the time-of-arrival discrepancy for a one-inch mismatch.
This PCB, like almost all of my PCBs, is a four-layer board. In my opinion, it is not wise to restrict yourself to two layers unless you’re dealing with a very simple circuit or you really need to cut costs. The four-layer arrangement is beneficial in terms of routing and performance: routing, because via connections to internal planes almost completely eliminate power and ground traces; and performance, because the internal planes allow for low-resistance, low-inductance power and ground connections. The extra top-layer and bottom-layer real estate opened up by all the internal-plane connections come in very handy when you need to provide a generous copper area for improved thermal performance (for example, to make sure that your LDO or your motor driver doesn’t overheat and enter thermal shutdown).
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