Playset Construction

Not sure if this is the best forum for this topic, but I tried to pick the most suitable.
We've got the corner of the yard all marked off for a large children's wooden playset.
I'm putting playground mulch around the playset after its built. I've mowed the grass down and sprayed roundup on the grass. Then I plan to put a plastic weed barrier down before the mulch.
I have two questions.
1. The areas where both sets of legs touch the ground are level with each other. However, the ground dips down in the middle about 3" in between where the legs are. Imagine a valley. Is it necessary to level this out with the rest of the ground or just make the mulch level? Keep in mind this will be where a little playhouse will be. If I need to level it out, what should I use? Packed pea gravel or other gravel?
2. What's an attractive but cost effective edging for the play area and to keep the mulch in? Landscape timbers seem to be the most cost effective but those start to look dingy after a year or so. Would it help to paint them?

Thanks for reading and the help!

 

Use 4 X 4's or 6 X 6's for the edging there direct contact rated, not at the tag on landscape timbers, there not.
The right way to install the timbers is to notch them so they over lap, then drill and pin them with 24" long rebar so there not going to move.
The weeds will just grow right through that landscape fabric.
The grass should have been rotilled and removed.
Round Up is not strong enough.
This would have been much better.
Pramitol 25E Herbicide, 2-1/2 gal. - For Life Out Here
Pea gravel is not compatible, you need real fill dirt.

 

Why would you want children near all those chemicals? I don't know about mulch either.

 

Well nothing is completed just yet, so I still have time to till up the grass. Thanks for the advice on the timbers. My main concern was leveling. I didn't consider just regular fill dirt. I just figured pea gravel or some sort of stone would be good for drainage. Fill dirt would probably be cheaper too.