the resolution limit of my telescope is around 0.7 arcseconds, so whenever my seeing forecasts show that seeing is 0.7 arcseconds, can I be fairly certain that my telescope will be performing at its limit on such nights?
Even if seeing forecasts were 100% accurate (which they are far far from) you would not be able to be confident of your telescope performing at its best -- not even on a night of perfect seeing conditions. There are too many other factors that can (and often will -- especially for less experienced telescope users) compromise your telescope's performance.
I've been using telescopes for more than 50 years; and I've never relied on seeing forecasts. I don't even look at them. They're that unreliable! Instead, I rely on experience. If I want to go out and observe, I go out and observe. I take my chances with the seeing conditions. And, strangely enough, with enough experience one's eye-brain system actually learns how to filter out the good from the bad even under seeing conditions that are so poor than one would have scrapped the observing session entirely when one was less experienced.
That being said, the two, perhaps most commonly used, seeing scales are the Pickering (or Modified Pickering) Scale and the Antoniadi Scale. Look them up! Practice using them, and eventually you'll be able to quite accurately judge the real-time seeing conditions while you're at your telescope.
But then there are other phenomena that can more or less mimic the effects of astronomical seeing -- at least until one learns how to tell them apart (experience and knowledge come into play -- once again).
There's really no end to learning when it comes to this hobby. This can be a source of frustration; but it can also serve to maintain one's interest in the long term. Some people enjoy learning new things. Some just want to see stuff -- and see it now. Some stick with the hobby for a lifetime. Some give up early on.
Knowing what's going on with one's telescope in real time, when it's being used, is one of the toughest things to learn when starting out: "Is the seeing bad, or does my telescope have poor optics, or is my telescope poorly collimated, or are my optics not sufficiently cooled down, or is my telescope suffering from tube currents, etc."
When first starting out, this is a complex, convoluted mess that's impossible to unravel; but with patience, with time, with experience, and with the right resources (such as a thorough star-testing guide) this mess will gradually sort itself out and you'll know what's going on. But there's no "instant" solution to this. It's going to take time.