DS1621+ & TS-832PX which one is better in my case

[vicentk]

First, my network will upgrade to 2.5G Wan. An intranet is a 10GbE connection between Mac Mini with OWC 10GbE with a wifi router. And now I'm using the Drobo 5C ( I have 6 pcs of 3TB HDD) and want to replace him with NAS. 

For this NAS, I hope it will: 
1: For Mac Mini ext-drive storage doc, photo and video in Raid 5 and a time machine, 
2: Sync the Baidu online cloud for backup.
3: Replace and sync google drive for accessing my business catalogues.
4: Storage the music in NAS and play it in Mac Mini.
5: Easy to upgrade the HDD size in the future.

Now I am looking at DS1621+ and TS-832PX, which are nearly identical in price.
1: DS1621+ without 10Gbe after add the second hand X540-T2 the price still in my budget.
2: Qnap, is it still easily a hack? (this very important because I don't want to waste time and money)
3: In my case, will 4gb run enough? If not, Synology needs ECC ram. It may be a little bit over budget.

Or you can advise the cheaper NAS that can fit my use. Thanks.

[ed]

DS1621+ will be a good choice. Qnap might require more configuring which also might be more complicated. Synology will do a better job guiding you through the process of securing your NAS. But both systems can be configured to be safe.
People only need 10GbE for video editing most of them time. Others are happy with 1GbE.
Having 4GB RAM is enough.

[vicentk]

Thanks for reply first.

Now I found out one more question, in my case I have 3 copy of data, one in USB hard drive ( daily use because my Mac min only have 512GB ), second in NAS/DAS, Third in cloud.

The question is is synology have any way to back up the USB hard drive, not using the usb copy because this usb is attach to mini.