I'm struggling with getting my Guerciotti fitted properly.

I started with 3ttt bars/stem (120mm) and found them to be too narrow, too low and too far (reach).

I have Nitto randonneuring bars and a technomic stem (80mm) now. I would have gone with a longer stem but the randonneuring bars have a longer reach than my 3ttt bars.

The width and height of the bars are great now but i'm struggling with reach vs handling.

The most comfortable set up right now is with the saddle all the way back. The handling is horrible. I imagine the handling would be better if i moved the seat forward but then i would need to move to a longer stem.

I'm a long distance rider that has gained weight. I would love to go long and low on the bars but need to find a comfortable medium while i work off this extra weight.

I'm considering a 100mm stem but trial and error gets expensive. recommendations?

As you move the stem up the bars are going to move towards you....It sounds like you got a double whammy with the stem length when you changed to a Technomic... You brought up the Bars which also brought them closer to you, and you lost 4cm off your stem....thats a pretty big change when you add those together...no doubt more than 4cm of reach was lost.

It seems like you already know what will help... move the seat forward and get a stem that's of similar height but longer. If you bought your Nitto Technomic from a decent shop they should let you exchange it for 100 or 110.