Russia has definitely considered Finland part of Russia in the past. I wouldn't be concerned about a Russian invasion right now if I were Finland. Putin is probably going to take a break to consolidate. Besides, it takes a few years for pro-Russian "civilians" to establish a large illegal presence in Finland and start agitating as a separatist movement. I'd definitely be on the lookout for that.

I wouldn't call people illegal like that. If Russian undocumented immigrants take up residence there and grow large in number then it's their right to decide how they are governed if they preferred to be part of Russia.

It's one thing to condemn Putin's actions but quite another to demonize immigrants.