The power decoupling caps: note that the primary function of these parts is to provide low-inductance power to the IC. The parameter to be optimized is inductance, smaller better; capacitance is somewhat irrelevant. Smallest case size gets you smallest inductance, both in the capacitor itself, and by the fact that you can place it closer. This is good for power integrity (reliability), and EMC. Of course, if you put a 0201 capacitor and place it 100 micrometers from the PIC power pins, it's overkill engineering. A 0805 capacitor 5mm away works equally well for such simple IC. But it's good to understand what the idea is to be able to expand it later when you have more demanding circuits.
Ceramic capacitor capacitance ratings are like "scams", when they sound too good to be true, they aren't; the available true capacitance drops under DC voltage bias. The smaller the case, the bigger the effect (obviously, a larger capacitor can store more energy; the smallest are "too good to be true"). But the unimportance of the exact capacitance plays the role here: if you decouple a 5V DC power source using 100nF capacitors of sizes 0402, 0603, or 0805, respectively, the effective capacitances might be something like 50nF, 60nF and 70nF, respectively (just ballparking something up as an example). All work for the purpose; but the 0402 provides lowest inductance itself, and can be placed closest to the power pin.
The requirements for the decoupling caps can change if you have special things like higher voltages, or large capacitive loads the device needs to drive. An MOSFET gate driver would be a good example; it works with, say, Vcc=12V, much more than your typical 1..5V logic levels. In addition, it quickly charges a MOSFET gate which might be 100nF equivalent. This charge needs to come from somewhere, quickly. So you would, as per example schematic, put there a 1.0uF capacitor instead of your bog-standard 100nF. Here you can expect there is a good reason to have that much capacitance, so you wouldn't pick the smallest and cheapest 0402 part because it could actually lose quite a bit of rated capacitance under such high voltage. So that could be a 0603 or even a 0805 part. Of course, instead of such handwaving, it is a better idea to look at the actual specs to verify these assumptions.
For all the resistors, refer to Ian's reply; actually do calculate the power dissipation!
I recommend you learn to hand-solder the components. It's simple: apply a bit of solder to one of the pads. Grab the component with tweezers, melt the solder again, while sticking the component in place with tweezers. Later solder the remaining pad. Home-brew reflow is the next step later, it will save time and enable use of some additional component cases (those with no apparent legs, but pads under the case), in more complex designs.
Larger parts may be easier to handle, but smaller parts make PCB layout work easier; you can actually afford more placeholder/dead space between subcircuits, for example; you don't need to escape traces far away from ICs, routing traces is much simpler as you don't have to avoid bunches of components. For example, if a 1.27mm pitch SOIC has power and ground pins next to each other, a 0402 capacitor fits right next to the pins, and the tracks leaving other pins around it do not need to take any detours. This also makes the circuit easier to follow by eye, with smaller components, the layout becomes closer to the schematic, components can be placed in the logical order because they fit better.
JLCPCB has this super-cheap assembly service now if you use parts in their parts library. Still, you can't avoid soldering, so it pays back to get a bit better on that. Despite, the process of ordering assembly is a learning process itself. I wouldn't invest time and money to that initially, only after you start feeling like you are bored soldering too much and want to pay someone to take part of the burden off.
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