Cisco is managed using IOS meaning you'll have to know some stuff on Cisco to configure it.
Your Dell PowerConnects will work fine for what you're doing. I'm currently using Linksys gigabit switches at my company. The last place I worked we were using Cisco Catalyst 6000 series.. expensive, yet very reliable for what we needed.
Stick with your Dell PowerConnects and you'll be fine. You don't want to mix up too much hardware if possible.
Those Dell PowerConnects are fine switches. Another option if you are unable to get more PowerConnects for any reason are HP ProCurve swiches. My workplace just changed over from Cisco to HP in our last set of infrastructure upgrades and I must say they are much more user friendly
Mainly we weren't using half the features of the Ciscos so HP was a much cheaper solution to do everything we needed.