Why did you an graceful exit when yiou want to continue with storj? Because your HDD was full? A full HDD is good in terms of profit for the space you provide. So I would try to rejoin the network, but i don’t know how that works. If you are only working for one satellite you get less ingress data. So it fills up very slowly (compared to other nodes), because you are connected to just one satellite.
It is recommended to run one node per HDD, as when the HDD is going to die you only loose the data that is stored on this HDD. However I remember it is not allowed to run more than one node per HDD. It is allowed to run more than one node per IP, but on seperate HDDs (it think that has changed, previous it was not allowed to run more than one node per IP).
When you are running 2 nodes behind one IP the network handles you like one node when it comes to ingress. So if your first HDD is full I would just start a new node with a new HDD, if that is what you want. When you start a new node, that node starts to getting vetted. During this time you will not get full ingress. That should take about 2 months when it is 2 nodes behind one ip.
If it is a good idea to spend money on a new HDD is a decision that you must take. Who knows how Storj is doing in one or two years? Nobody can tell. If you decide a new HDD you shouldn’t take a HDD with SMR, you should take a HDD with CMR or ECMR. https://en.wikipedia.org/wiki/Shingled_magnetic_recording
You could also start a new node with a smaller HDD that you might have around without buying a new one and once that is full you can migrate that node to a new HDD. There is a guide in the documentation an how to do that. This would be a smart option, getting the new node vetted and when you are thinking that it could fill a 16 TB HDD and you are willing to invest into the project than you could that.
I can’t tell how long it would take to fill up a 16 TB node, as who can tell what happens in the future. But I would guess it would take something between one and two years. Thats for one node behind one IP. That should also be true for one full node and one node filling behind one IP (thats how I understand storj works).