I don't use the exchange, but I imagine you can easily remove whatever you don't like. The game comes with a built in lot editor even if you don't have the CAW tool. The only thing you can't remove are roads and unbuildable terrains.
the problem with the editor is, the included towns don't really have room to make new lots, you can fit a couple in, but the terrain is either not flat or there is other features in the way.
that is why i went with the flat map..
you do need to enable a cheat to add the collectible spawners if you want them in the town however. but it just takes a few minutes.
as for the exchange, i just use the "save file" link in the descriptions to download it instead of using the craptastic download manager.
haven't had any problems with the lots or worlds/towns but downloading actual sims has messed up a couple things, especially skin textures.
so now i have nraas / twallan's story progression make the sims for me, been using that one flat map for 4 games now. and i build a few houses and fill a street or two at a time with a couple different houses.
works really good for me.. i think i did have to add the junkyard and consignment shop in the beginning, possibly the dance club, but the job related buildings are there. and about 100 empty lots means you can do a LOT of customizing. --- i tried being serious once, in 1989.. didn't particularly care for it.. so don't expect it to happen again.
found a really good one to start completely from scratch..
just a huge map (possibly to big) with the roads, some empty lots, just a few trees (like 20 total) and about 3 big rocks at one intersection. you could even remove the trees and rocks, would take about 5 minutes. there is a couple small hills in the big open spaces. but they do not interfere with any lots, or even come at all close to them.
it has NO buildings at all. i actually copied a few from parkwater flats, mainly the "mall" since it's so handy to have 5 businesses on one lot. or you can build your own.
it's called "giant basic map" http://www.thesims3.com/assetDetail.html?assetId=3370252
i believe you will need to add spawners if you want any collectibles in the town.. but that's easy.
maybe i should have cleaned out those few trees, added the businesses, a couple parks and spawners then saved it like that.
i really like it, i put in the businesses, including a larger version of the junkyard, put in about 15 houses of varying sizes, i only moved created sims into three of the houses, two houses with my friends from real life and one for my sim.. the rest i'm letting nraas's story progression fill up. plus this time i'm not assigning any jobs, besides my own sim. also no celebrities or vampires so far.. tho i do have saved sims if i do decide to add either of those. --- i tried being serious once, in 1989.. didn't particularly care for it.. so don't expect it to happen again.