QNAP TS-420 Setup Query

Hello I would be grateful for a little help regarding my QNAP NAS drive. I bought the NAS in 2014 along with a Naim NDX from UHES who were very helpful but are no longer in business. The NAS was set up by the dealer with two 2.0 TB WD Red hard drives in RAID 1. At that time I had a Windows pc and used dBpoweramp to rip my CDs to the NAS and it was set up with TwonkyMedia server. I now wish to start again and re-rip in a lossless format to the NAS and I now have a Mac computer. I have downloaded the Apple OS version of dBpoweramp CD Ripper. Before starting I would welcome a little advice so I can optimise my ripping and storage.

1. My 2 hard drives are 3-4 years old so would it be safer to ditch them and buy a new set or can I expect them to last several more years? Would it also be better to buy one or 2 additional disks so as to upgrade to Raid 5,6 or 10. Perhaps I should even keep my 2 existing disks and then add 2 new ones with RAID 5 or 10? There is so much conflicting advice on line and a lot of it relates more to complex business systems than a small home media setup

2. The QNAP software includes various apps such as Media Station, Music Station, Photo Station and TwonkyMedia. Should I keep these apps or is it better to remove them and just make my own folders for Music, Video, Photos etc?

3. Which is the best UPnP server for use with the iMac - AssetMinim seems to have a lot of supporters

3.Are there any recommended settings for dBpoweramp? it seems to rip to FLAC but not WAV - I believe I can convert "on the fly" but I am not sure how

Apologies for all these questions.  I am getting out of my depth streaming technology and I have searched around the internet first for answers

Bob