I walked the stages I've done between early spring and October.
I think the Camino Frances is extensively walked and if you go between easter and September there will definitely be plenty of people around.
It was lovely walking in October but unfortunately a lot of accommodation was closed so I ended up struggling to find anywhere a couple of times (I never booked far ahead as I wanted flexibility about exactly when to stop for the night 😳).
I stayed somewhere really nice but expensive a couple of times when I couldn't find anything from the guidebook - one time I stayed in a guest room above a restaurant which was hosting a wedding on a mountain - I stopped for a very late lunch on the terrace and phoned everything in the guidebook looking for accommodation that night and everything was closed! So I asked the waitress and she said a wedding guest had cancelled and I could have their room, so I did...It was lovely but over budget (and cowbells were ringing all night).
I can't start again until Easter because I've got to the Allgäu and most of the accommodation reopens then.
Mind you in this unseasonable weather I'm pretty sure the season could be safely extended.
I walked some early stages with a local friend but she's a single parent so once I was staying away overnight I started walking alone.
If I'm honest I very much prefer to walk alone, though I guess my preference would be walk alone and meet up each evening ☺️
I have rarely felt unsafe walking alone tbh. So far anyway! Obviously it'll depend a lot on the location.
I often walk in places where I don't see anyone for an hour or so (both on the Camino and near home) and don't feel unsafe, but places have a feel don't they - I've also unexpectedly felt unsafe on just the odd occasion and made sure my location tracking is on and that my family know exactly where I am, and picked up my pace, made sure I have my sticks in my hand (usually I leave them in my pack and only use them for very steep downhill stretches).