First schematic - Critique my ATMEGA-328P design
Add three 0.1uF caps from VCC and AVCC to Gnd. Install them near the pins as possible.

Add a 0.1uF cap from Aref to Gnd.

Add a diode from Reset to +5 (cathode to +5) to keep any spikes on the reset button way from reset (can make the chip think it's going into High Voltage Program mode and then look hung).

Add an FTDI header so you can connect to a PC via a USB adapter (like FTDI Basic) and download code, and debug via serial print statements. The signals needed are PD0, PDI, DTR, +5, Gnd. DTR connects to Reset thru a 0.1uF cap; DTR goes low, the cap and the 10K Reset pullup make it a pulse to kick off the bootloader (if loaded). Also helpful to have a diode between +5 from the FTDI (anode))and the output of the regulator (cathode) so the regulator can't back drive 5V into your PC if both supplies are connected - PCs often don't like that and can shut down the USB port.

If you're worried about the load on SCK for an external chip trying to drive the pin as an input, change R3 to 2.2K or 3.3K, the LED will still be plenty bright.