Yes this is plausible!
There's two main constraints that limit the size of terrestrial animals: Their ability to breath and their ability to walk around. Neither of these prevent arthropods from getting as big as what you describe, which we know because of examples of giant arthropods alive today and in the fossil record.
Insects and arachnids lungs aren't really built to scale up to to large sizes, but some arthropods can. As Daron has already pointed out in his answer, coconut crabs are terrestrial arthropods that can be over a meter long. They have a very unique type of lung - but the point is that it is plausible to have giant arthropods with functional lungs.
The biomechanics might seem problematic, but it actually isn't. Your giant bugs would not move as rapidly as their smaller counterparts, just like you'd expect any giant animal. But arthropods that large and larger are more than capable of moving around on land. Coconut crabs aren't very fast but they are quite mobile. They can climb trees and are known to occasionally kill birds and small mammals.
Perhaps the main reason that arthropods don't get extremely large nowadays is ecological, not anatomical or physiological. It's not that arthropods can't get that large, but it's that vertebrates are better at it, so in general small vertebrates can outcompete giant arthropods for those ecological niches. Looking at the fossil record, before vertebrates got good at moving around, arthropods got truly enormous. For example, the largest known terrestrial arthropod ever is the 2.5-meter-long millipede, Arthropleura. During the same era (the Carboniferous period) there were famously also giant dragonflies over 2 feet long. At that time, there was more oxygen in the atmosphere, but only about 60% more than at present according to wikipedia. That could account partially for the giant insects - but 60% more oxygen by itself wouldn't allow them to be several times larger than they are today. To get arthropods that large in the modern atmosphere, you'd just need a way to get them 60% more air than their Carboniferous counterparts. Since you're not looking at flying insects, their energy needs are not as great as a dragonfly, you can probably get away with less. If you're OK with them not being extremely fast, I would say it is totally plausible for giant bugs to be as large as you describe.
While we're on the subject of large fossil arthropods, aquatic eurypterids are very similar anatomically to scorpions (they are probably closely related to arachnids). They got to lengths upwards of two meters, and fossil trackways show that some species (including the big ones) walked around on land occasionally. The limiting factor on their terrestrial motion was their inability to breath air, not the difficulty of walking itself.