It will be very difficult for the Gnome, even with a 100% build; that's a fact. I've been defeated many times, and it creates a great matchup: MONSTER vs. MONSTER!
Added after 47 minutes
If you still decide to play as a Necromancer, first read the last 2 pages of your own thread – "[PROBLEM] Which faction is the hardest for Gnomes to play against?" Then analyze it and express your opinion!