Few steps here. Firstly buy the comics to support the artist. Then after that, there are a few ways to have a digital copy which you can store on your NAS.
comic/manga/manhua/manwha, can either be in CBZ, PDF, ZIP etc. But if that's not available (from official sources), you can use something like these downloader apps to obtain them
https://hakuneko.download/
https://github.com/dazedcat19/FMD2
it's recommended to store the folder with the images as a compressed file in either CBZ/ZIP/RAR/7ZIP of your choice. Then store that on your QNAP NAS. On the NAS, create the share and sub directories in a way that is easily understood by you so you know where your stuff is at. Also remember to backup
Next step is viewing from either mobile (android) or desktop pc (windows)
For android, my recommendation is comicscreen (it now supports smb 2/3). has some ads, but within tolerable levels.
https://play.google.com/store/apps/deta ... omicscreen
For windows pc/laptop, my current recommendation is YACreader which is open source (previous recommendation was CDEXdisplay, but it's rarely maintained and has some bugs)
https://www.yacreader.com/
YACreader can be used as a standalone reader to open up those compressed files to read. But it also has another app called YACreaderlibrary which you can use to create libraries of your comic/manga collection.
if you're too lazy to manage that, you can just simply read online
https://mangadex.org/
https://www.asurascans.com/
but if you have a NAS, and you want your collection to be available regardless if you have internet or not, then i suggest storing your own digital collection on the nas.