I'd prefer 4 months to 8/12 weeks.
Am always conscious that typing on t'internet seems confrontational, not intended that way at all ...
Is there a particular reason you would prefer 4 months? Do you have a perception that the puppy will come part trained and will therefore be easier?
In some cases this can be true, in other cases it may well be entirely the opposite. I think Shibas are a 'clean breed', so perhaps house training won't be an issue, but general training may well be more difficult.
Puppies need to be socialised before they enter fear periods. If you genuinely have a breeder who will be doing all that for you - taking the puppy out on its own on the lead, getting it used to the car, making sure it is confident without additional canine company - then this can be fabulous. If not, you can end up with an over-boisterous or neurotic mess.
Oh, and further to that point - I say I have two imports. I drove out to see them (one from Germany, one from way down in France) at 8 weeks to make sure I was happy with the temperaments on the parents, with how the breeder kept and handled their dogs and with the puppies. I then drove back out to get them when their passports were valid to bring them back to the UK. Puppies should never be 'mail order'!