It's possible to swap your plate body for RS Gold a fighter torso, unless that you require the additional defense (which is probably not the case), and I think torag's plates provide the best defense stats as far as barrow's legplates are concerned.

The setup you have will be perfect for taking on. The only changes you can do is to add a Skillcape and Soul Wars Cape, and the Chaotic Rapier. If you're planning to buy Fury / Bandos I'd suggest getting the Fury first, as it's the cheapest but also it has better bonuses than bandos Tassets. Have fun.

I'd honestly say there's no one skill you can train to be a good one. All of them are valuable to some degree, and the only thing that training one will do is hinder you in the long run. With that said here are some suggestions and the reasons behind them:

Construction. If you have an entrance room, a menagerie, and even a prayer altar, this is very helpful. The portal room is useful, especially in the beginning of your time as a member and most of the teleports you'll use are there. The POH is also great to store items, including every tool, all books, and a lot of other clothing and armour.

Agility is also very useful and achieving it at least 21 is vital so that you can utilize the Varrock-Edgeville shortcut. And getting it higher can be extremely beneficial in RS 2007 Fire Cape running through monsters, large quest areas, as well as PKers (true experience here). Achieving it to 21 should be one of primary things that you do.