That's a bit pricey on the slider hitch installed (I'm assuming it's manual). You can get them for about $800, so do you think that the install is worth $400? That's the same as the one I have and when I negotiated the deal, I had them include the hitch and installation.
BTW, my 5er is made by Forest River and it is a decent unit. ALL trailers have their share of flaws, but it sounds like you got a great deal! Congrats.