Yeah, the 1050 Ti isn't going to be particularly good for rendering most graphically-demanding games at 1440p resolution. A graphics card needs to render significantly more pixels at 1440p, and in general that will cut about one-third off your frame rates compared to 1080p. So, for example, if your frame rates were hovering around 60fps in a particular game, moving to 1440p would likely bring them down to around 40fps. Or if you're at 45fps, it could drop you to around 30fps. So, gaming at 1440p probably isn't going to be ideal without a somewhat higher-end graphics card.
You might also consider looking at a single, higher-quality 1080p screen, rather than two lower-quality ones. What monitor do you have now, and what ones where you considering getting? As was pointed out, you could reuse your old monitor as a secondary display for use while streaming.
Also, why are you considering buying a new motherboard? That won't likely do anything significant for performance, and I wouldn't bother unless there is something wrong with the one you have. When you eventually decide to do a more thorough system upgrade, newer CPUs will require different, incompatible motherboards anyway.