You may be able to do better buying a pre built pc but, I applaud your desire to do a build yourself.
The experience will be worth whatever you pay.
In addition, you will know enough to troubleshoot any problems that your parents encounter.
Without access to your shopping, here are some principles.
1. Start with a good monitor that can display a 4k image.
It need not be large. 24" or 27" perhaps.
The reason for 4k is to be able to display photos with close to the detail at which photos were taken.
The monitor should have the modern Displayport input.
2. Use a ssd for windows and storage. A ssd makes everything you do so much quicker.
It need not be large 240/500ay well be all you need. If you will store large video files, a HDD is a more economical device for that.
It is easy to add a hdd later.
Do not buy a cheap ssd, not all work well. You can be safe with a Samsung EVO for performance and reliability.
3. Processor.
Pick a current gen ryzen or intel processor.
Really, any will do, even the cheapest will have sufficient power for your needs.
On the ryzen side, pick one with integrated graphics like the 2200G
On the intel side, they will all come with adequate integrated graphics.
G5600 is a quick unit that would be appropriate. I happen to like Intel better.
3. Motherboard.
You will want a supported motherboard for either ryzen or intel.
You will have a choice of size format.
Itx will have one expansion slot and often comes with integrated wifi.
M-ATX will have 4 slots and ATX will have 6.
You are unlikely to ever need more than one expansion slot, perfhaps for a gaming discrete card.
The advantage of a smaller motherboard is that you can use a smaller case.
4. Your processor will come with an adequate cooler.
5. Sound.
A modern motherboard will come with integrated sound.
If music is not a priority then a inexpensive pair of desktop speakers will do.
If your monitor includes speakers, you can use them.
6. You only need a minimal wattage for the PSU.
Stronger power supplies are needed only for discrete graphics cards.
Quality is all important, do not go cheap on the psu.
Seasonic is always good, I like the focus line. 450w is very good.
7. You asked some questions:
- no discrete graphics card will be needed.
- If you value anything on the pc, you should have a usb connected drive for backup.
- 300w is sufficient, but a stronger psu will only use the power demanded of it regardless of the max capability.
- The processors we are talking about all come with an adequate cooler.
- On wifi, you are ok if wifi is included with your motherboard. therwise consider a pcie add in card with a good antenna; They will likely have better signal strength.USB wifi dongles will work, but may not be as strong as you need. Check user experiences
- If your case has room for a dvd drive, buy a sata connected drive. If the case does not have room, a usb attached dvd burner works equally well
- A ITX sized motherboard will fit only a ITX case. A M-ATX case will fit either a M-ATX motherboard or a ITX motherboard. A full ATX motherboard needs a ATX case.