The city has cut down my dead ash tree and are coming to remove the stump (I believe by grinding). They have advised me to "remove landscaping features" so they aren't destroyed in the process. How far out from the tree do I need to clear? How soon will I be able to replant there?
Landscaping features are anything decorative in the vicinity that could be damaged by all the equipment. This includes things like rocks, bird feeders/houses/baths, edging, statues, that type of thing. Even small shrubs and perennials can be temporarily moved. Also, if you happen to have landscape fabric down around the area where they will be grinding, move that. Is is a mess when grinder blades find it.
How far out from the tree to clear will really depend on the size of the tree. An ash tree doesn't generally have lots of large diameter surface roots (some do, most don't) and that will partially determine the area they will need to grind - They often follow out a big surface root and grind it out, so if you see any, clear everything away from them at east 2' on both sides. Also, if the stump is big (2' or more in diameter) I'd clear at least 6-8' on all sides, if possible. It's nice to be able to maneuver around the stump easily without being afraid of crushing something. It also depends on their grinder - what size it is.
When they are done, there will be a rather large amount of chips mixed with soil, even if they clean up some if possible. What you want, before you plant, is to clean out everything the grinder cut out, even the soil (because it will be mixed with grindings). Then you want to fill the hole with quality topsoil and tamp it well. Follow this link for a more detailed guide on how to clean up stump grindings. If the stump is in a mulched bed, disregard the part about sowing grass seed.
If you have tamped the new soil in well, you can plant right away. If you aren't able to, wait until it rains, and topdress with more soil if necessary. After it's planted, mulch it to build the soil, keep weeds out, and conserve soil moisture. Whatever the case, give yourself plenty of time. Some stumps take even me half a day to properly clean out.
In terms of replanting, once you've cleared away any debris left behind (there's usually a fair bit, and if you haven't requested they take all debris away, there'll be a lot), dug the area over and added something humus rich, a week later and you can replant.
As for 'landscaping features' I'm not sure what they mean by that, and that's something you ought to ask them, really. If they're bringing in a stump grinder, that's a piece of machinery, and they'll use whatever access they can to get it in the garden, then they'll probably work in an area of, say, 6 x 6 feet at most. They may also bring in a chipping machine to grind up any larger bits of wood, so again, an area might be damaged by that (lawns particularly) but you really need to check with them precisely what they mean. If you have any pots or statuary or lighting nearby, its probably safest to move those out of the way, but otherwise, unless they're suggesting you dig up any plants within the vicinity, it's hard to guess what they mean.