I’d go for it, especially at that price – & Turner back up is superb.
Seatpost is 30.9mm diameter.
Frame should come with instructions showing how to mount front mech & if its a Shimano how to trim a lug off the mech to stop it fouling.
Take off the mech hanger & give it a good greasing on the mating face with the rear dropout – lots of people have had issues with creaks on DW Turners, myself included. Turner will send parts straight away but it didn’t cure mine – traced to the mech hanger in the end & I’ve heard of other cases too.
As for cables I went for basic Shimano full length outer & standard SS inner’s but with Middleburn Cable oilers about 2-3″ from each shifter & one on the chainstay above the DW-Link decal on the rear mech outer.
Thats a good price, well below £RRP so treat it to a new headset & get the shop to face the head tube & BB shell, & install the headset cups for free.
Some DW Turner owners also change the top shock eye bush for a roller bearing from Real World Cycling;
http://www.enduroforkseals.com