Many thanks for your helpful reply to my query.
You are correct on all of your points and decisions IMO.
If you answer a scam call, your number is marked as 'active' and you will receive more calls. They will keep calling indefinitely in the hope they will get to talk to someone who will listen to their scammer script and be taken in by what they have to say.
Ideally, let the unknown scam calls go unanswered. When the line is silent upon answering it just means when the automatic dialler has connected your call there was no human scammer at the other end available to talk to you so the line is silent or disconnects. The scam diallers can also detect an answering machine response so that is actually the same as answering the phone in person in determining an 'active' line and the calls will persist. Turning the answering machine off means the line keeps ringing out. If the line is never answered it is likely your number will be demoted for attention from the scammers. The auto diallers also work through particular blocks of numbers so you may get periods of greater and lesser scam calling.
If you don't get that many scam calls, see if your existing phone has a 'VIP' feature on it (terminology varies between manufacturers). This is basically a 'tag' you can apply to contacts in your phone contact lists (tagging the name as a VIP caller). Once a caller is tagged as a VIP, some phones then allow you to set a specific ring tone for VIP callers. If you hear the VIP ringtone, you know it is someone known to you without having to look at caller ID on the phone. Leave anything else to answering machine (or preferably ring out unanswered).
Some phones also have a 'do not disturb' feature which will keep the phone silent when you activate it (either manually or for timed periods in the day). On some models VIP callers can be set to break through the 'do not disturb' period so your phone should be silent unless a VIP caller breaks through the do not disturb setting.
Your existing phone may have other features to help. Just depends on your phone make/model.