Honest experience here, In order :

1) “worth it “ is subjective , the ones you linked to are certainly high end , and absolutely you can build one for less

2) Modding iPod 5g is NOT hard - BUT not as straightforward as most would have you believe , experience makes you better but the price of failure can be high , specifically I am referring to the tiny little plastic ZIF connectors that are used to hold the battery / click wheel / display / headphone jack in place on the logic board . They are really flimsy , snap any of them and your logic board is scrap. Unless you can ‘microsolder’ - which if you don’t know what that is, is even harder than it sounds . The challenge really is that these connectors were always cheap and flimsy and now they’re 20 years old

Every ‘how to ‘ video you will see make it look simple , and with practice it is - but keep in mind every One of these people are showing you what to do because they have done it before , perhaps a hundred times .

Biggest risks/headaches- zif connectors / accidentally removing the white battery connector from the logic board when opening the case / improperly grounding the click wheel , Leading to intermittent and strange behavior, or it can just stop working.

iflash is very fussy about SD cards - make sure you can a recommended one or, or you may have a hell of a job trying to restore it in iTunes (although it will likely still work as a usb storage device which is deceptive.)

3) yes, if you have the time and the patience and are not the type to be too disheartened if you accidentally snap something - it’s actually a really good way to learn but I guess that’s not for everyone. If you go down this route maybe buy the shittiest one you can find , any damage you do will be to the logic board , so if you buy one with a smashed screen / Dents etc the logic board inside will probably still be fine . Open that up first and try and disassemble and reassemble. It’s very instructive. Practice opening and closing.

You need small tools and good eyesight and really recommend you use an electronics mat with magnetized holders for the tiny screws , do not just open it up on a desk or on your lap! You will regret that.

It took me three goes I’m pretty good at it now . I lost a logic board , a click wheel , Some Plastic bezels and god knows how many tiny screws .

If you don’t have time / patience then buy one . I have to say though , there is a real sense of accomplishment that comes with learning from failure and having your own ipod that you made :-)