1- really depends on the volume you want. A huge volume, give it a few months. If you're doing ~100-200/day, can get away with a month... I'll also throttle up the warming functionality when I start to email
make sure DMARC, DKIM, SPF etc is squared away
2- I usually just network & use LI
3- no, I would advise you to not do this. It's so easy to do now, not even worth it