There are many discussions in this forum about cutting back large, overgrown rhododendrons. In brief... They can be cut back to 3 feet. How quickly they grow back or if they grow back at all depends on a number of factors including variety of rhododendron and how much sunlight it receives. In any case, regrowth will most likely be slow; years rather than months. A hedge trimmer would have a very difficult time cutting through tough woody stems and would mangle the cuts. Hand pruner, lopper and pruning saw are the proper tools for the job.

Rather than cutting back to some arbitrary height and then having to wait a long time for the plant to reflush and look decent, I'd suggest you leave it at that height but prune out some of the side branching at the base to convert it into more of a tree form. If pruned in that manner, it will provide a nice contrast in both height and texture to the maple and look like it is intended rather than just overgrown. You can then accent the base with some attractive rhody-friendly groundcovers.

The alternative is to move it to a more suitable location. Cutting the shrub back to very low level or a regeneration pruning is not going to provide you with anything appealing at that very visible entryway for at least 3-4 years, perhaps more. In fact, it will be an eyesore!! I routinely encounter or suggest hard pruning of rhodies - it's pretty common in my area and most respond well to the practice but it is a very slow process.