Hi Foxy,
first of all, congratulations, it's a good looking team, and you're well placed to achieve your goals.
I think you need to make 2 trades, and then wait and see what happens.
My own opinion is, that NicNat is cooked. I will be very surprised if he plays too many more games this season, and if he does, whether he'll post any meaningful scores. They don't achieve much by playing him. Mathematically, they can make the finals, but form and draw-wise, they're done for the season. I know what Worsfold said about no early surgeries, but that will change with another loss or two.
You may be suffering from "paralysis by analysis". In other words, over thinking things so much, it makes it nearly impossible to make a move, let alone a confident one.
Your analysis of your team is pretty much spot on. You need to fix your D6, and your R2/F6. You've got some great DPP's set up, and I wouldn't be too concerned about missing the D/M link.
Looking at your tradeable players, I would list it as:
Terlich, Clisby, Viney, NicNat, Nicholls (Gawn would be here too, but it's not unreasonable to want him at R3). Looking at their prices and B/E's:
NicNat - $450,200 - 132
Terlich - $416,200 - 133
Nicholls - $401,900 - 125
Viney - $284,500 - 53
Clisby - $243,700 - 23
The bottom 2 aren't going to lose much, the top 3 will drop in price at their next game, and have injury queries.
I don't think your concerns about Shaw are justified. He is the obvious choice for Def Prem. I think you'd be more worried about Dixon, if you got him in. There has to be some doubts about him getting through the season from here.
I think there is no need to sit on cash for now. Don't be afraid to use what you have, if it makes 2 genuine upgrades. I don't often suggest the obvious players, but in your case it really looks like you'd be best served by Shaw and Goldstein. They cost $1,036,400 and subtracting your $355,800 means we are looking for $680,600 to get them both in. Even though Terlich will drop a little cash, and Clisby will still make some, I think if Terlich is picked this week you trade NicNat/Clisby to Goldstein/Shaw. Terlich doesn't go under 70 too often, and Clisby doesn't go over it too often. Terlich makes a much better D7 for you. With Hanley still out, you can look at Terlich's score and decide between him and Staker. That's pretty good for D6 until Hanley is back.
From there, I'd wait and see what's happening with Nicholls. You don't want him to lose too much cash before you turn him into McBean. This will give you the cash to turn Viney into Jack K. and leave your team looking like this:
Def: Goddard, Heppell, Gibbs, McKenzie, Shaw, Hanley - Terlich, Richards (+ Staker)
Mid: Ablett, Pendles, Swan, Jelwood, Danger, Barlow, Fyfe, Jack - Mitchell T, Neade (+ Walker, Rocky, SJ, Bartel)
Ruc: Goldstein, Minson - Gawn, McBean (+ Cox, Rowe)
Fwd: Walker, Cox, Bartel, Rocky, SJ, JJK - Staker, Rowe (+ Neade, McBean, Richards)
That's a very strong looking team, with good coverage. You have at least 2 useful back ups on every line, bar your Fwd line, and lots of loopholing possibilities. That Fwd problem might be your "weakness", and why you'd keep that trade up your sleeve. If it really concerns you about the back up, bring in Harvey instead of Jack. You then can loophole him and Mitchell, and he covers 4 of your starting 6 Fwds in case one is out, and Staker is needed elsewhere.
I'd wait on doing the Nicholls McBean trade a week or 2 if you can, just in case things go pear-shaped. Keep an eye on the prices, so you are sure you can get the Viney upgrade that you want.
From there, I'd hold the last trade and the $30-40K until the last week, just in case.
I hope this helped, even though it's not very imaginative. Sometimes, for some Coaches, the obvious picks/suggestions are obvious for a reason. You have the opportunity to bring in the number 1 Ruck and Defender. There doesn't seem to be a good reason to not do it.
Good luck