Electronic – Schematics vs PCB designs

With a common collector configuration the output voltage can never be larger than in the input so you will be limited to the 5V output of the Arduino (minus 0.7V for the bBE junction).

So the most appropriate is a common emitter.

You need to control the base current with the common emitter so use a resistor from the Arduino that gives about 1/10 of the collector current. Since you have a 700mA LED that will need about 70mA base drive which is too much for the Arduino (can only supply a maximum of 20mA).

You could use a darlington connected transistor which has higher gain, for example a TIP120. You could run that with just 1% of the collector current into the base - i.e. 7mA. A resistor of about 470 ohm would be good. Alternatively you could use a power MOSFET, select one with a logic level gate drive as you only have 5V from the Arduino. A gate resistor is not necessary. The resistor in series would need to be (24 - 3.4)/0.7 = 29 ohm. This resistor needs to dissipate ~15 Watts so it will need to be a large wire wound one or multiple resistors in series/parallel to dissipate the heat - it will get hot.

Since you have 24V to power the LEDs it is better to put the 4 LEDs in series as you have shown. You will only need one series resistor and the total power consumption will be less as lighting all 4 LEDs will take just 350mA - if you put them in parallel they will take 1.4A. The total voltage is about 12.8V leaving about 11V across the resistor. This resistor should then be 31 ohm (about the same as the other one). It will only dissipate ~4Watts so doesn't need to be as large as the other.

Using 24V this circuit is not going to be efficient as most of the power is dissipated in the resistors. It would be better if it could be driven from 12V or 5V. 12V would probably not be enough to drive the 4 LEDs in series so they could be split into two groups of two. With 5V each LED would get its own series resistor.

For a great deal of extra complexity you could increase the efficiency by driving the LEDs from a switching supplies.

I have not traced every link you've sent, but here are some basic rules that should help you. Mind that some folks will guide you differently, there are some claiming to keep different ground planes and connecting them on a single point. That's possible to implement but much harder IMHO as it is more important to make sure that all fast signals have a ground plane under them without any exception. Separate ground planes only make sense in power electronics where you could create ground bounce issues without the separation. For fast digital systems, decoupling and good ground planes are more important.

In order to understand this, think of impedance at high frequencies in combination with return paths through the path of least 'resistance' (=impedance).

A fast signal has it's return path right underneath the trace on the ground plane. No matter the thick fat copper you might have elsewhere. If that return path is broken by split power planes or any other cause, the signal does not follow the smallest loop to return and instead creates large loops that radiate. Same for the power to fast devices. If you do not decouple these properly by placing ceramic caps very close to the power pins or by not having low inductance via's to ground plane, then you have the same issue with power paths.

Other than that, keeping analog and digital stuff as much as possible separated is good, also running digital and analog traces perpendicular to each other. If you have switching power supplies for analog circuits, yes keep them on the digital part then have them filtered (RC, LC or LDO) and pass through to another plane or area.

Mixing analog and digital is not that bad if you understand good design for avoiding EMC issues.