Maintenance for the week of April 15:
• [COMPLETE] ESO Store and Account System for maintenance – April 16, 8:00AM EDT (12:00 UTC) - 6:00PM EDT (22:00 UTC)
If you only care about doing normal dungeons and overland content you can just use any gear that you need, but for veteran content you want to use a build that isn't, to put it nicely, bad. There are a lot of people who say that they can do any content with builds from fextralife, xynode, hack the minotaur, .... but those people are either not pulling their weight or are just straight up lieing.
Now for your questions:
1. I dont know why you would want a guild for only necros. if you are looking to improve with your damage or have questions about your build, you could join a beginner friendly pve guild
2. For starter gear I would recommend mother's sorrow + julianos + illambris/Maw of the Infernal/valkryn skoria/ you can farm mother's sorrow in deshaan or you could buy it from guild traders. you can craft julianos in wrothgar or buy it from guild traders. and you can get the monstersets from crypts of hearts (CoH) 1/ The Banished Cells (BC) 2 / City of Ash (CoA) 2