Hi as topic...I plan to upgrade my 8 years old macbook pro from 128GB to 256GB or bigger..Below is my question:
1. Is better to source used 256GB SSD from scrap macbook?
2. Understand it using PCIe-based SSD but the connector is not same as typical PCIE right...?
3. Linking to question 2, once it upgrade, I heard some function including Hibernate will not work unless you restart the machine, it is true???
4. Free software to migrate everything from my current SSD to new SSD? Or better format? If format how?

Sorry ah too much question but I think is the right time to upgrade even currently I utilise 60% of the memory.. ><

Do you plan on migrating it yourself? Or you prefer to get an expert to do it for you?

1) Usually if you plan on that, you can opt to search on eBay to find the right code for the SSD
2) You would need to find compatible SSD, you can refer to OWC (https://eshop.macsales.com/shop/ssd/owc/macbook-pro)
3) I have upgraded my old 2012 Mac Mini and also 2014 Macbook Pro as well, never had issues with Hibernate
4) I have used this in the past - https://bombich.com/ (Carbon Copy Clone)

Will migrating my self.. or any expert can recommend?

Message MacCore who is also here in the forums. They will do a good job for you.

https://www.maccores.com/

Again..what ssd you using during your upgrade?

One was a SATA SSD which was for the old Mac Mini 2012 and the other one was a AData SSD. Honestly it was quite a while ago that I forgot the model already as I have since sold the Mac.

Ok.. I plan for buy the connector to convert normal PCIE SSD into macbook connector..Not sure it last long or not...