Devices with official LineageOS support will get OTA updates. Newer devices with A/B partitions will even get seamless updates like stock, where the update is applied in the background and the user just needs to reboot to use the new version.
Yes, but official LineageOS can be dropped without notice. And even if optimistically a popular device will not drop support until it's too old, the blob is still not updated and the linux kernel is not usually mainlined. Many exploit on that. And let's not talk about the blobs are not open source. That's why there is a demand on Linux phone which the kernel is mainlined and up-to-date.
Again, ignore the fact that iPhone is closed source, it does provide a infinite software update until it's broken, which is better service than most Android phone, even if considering installing ROM.
While support can be dropped without warning it's unlikely to happen once a phone gets ported to a LOS version. Usually it s just that the phone gets dropped when LOS drops that version. Hence the key thing to watch out is whether the developer is porting the phone to newer versions of LOS when they become available.
P.S. If/When they do and you use LOS be sure to tip LOS and the developer ;)
