Just wanted to provide an update. Thanks to everyone for their input. I ended up getting the 18-135, the 1.4x TC, and the 300 f4 all for just a tiny bit over my original $1K budget - all used, from the forum marketplace. They have all finally arrived. I love the size and versatility of the 18-135. I am very happy I didn't go with the 150-450 - there is literally no way I could carry it around and use it without a tripod for any significant length of time. The 300 + TC is already a lot heavier than my current setup, but I think it will be manageable with a new cross-body strap. Unfortunately it's been dark by the time I get home so I won't be able to test them properly until the weekend.
Preliminary indoor tests demonstrate the 18-135 appears to have no obvious front or back focusing issues, solid AF that is fast and so quiet, and is sharper than my 18-55 DA L and 55-300 DA L at all lengths, although the difference is less between the 18-135 and 55-300 at 135 than between the 18-55 and 18-135 at 55. The 300* is not well suited for indoor shooting (my house really isn't that big!), but has quick, silent, and accurate AF and is clearly sharper than my 55-300 at 300. With the TC attached, the AF focus often does a lot of hunting, but is accurate once it finds it and I can't see any loss of sharpness. Fortunately, the manual focus ring is very easy to use without having to press any buttons and very accurate in the lower light conditions where the AF was struggling.
So far, so good!