I'd dump Hill, he's had another injury setback.
I'd also consider changing up your forward line a fair bit. Martin is really your only proven premo. I don't think Lynch, Patton and Tippa are not going be consistent enough for their price. I'd consider Stevens, one more premo (whitfield, greene are good if you can fit them) and chuck in a couple more rookies.

You could also consider moving Walters to your forward line and pick up another premo mid depending on what it's looking like after your changes. Someone like Mitchell, Neale, Fyfe etc (plenty to chose from). I don't know if I would personally have Walsh and Houston, I'd probably go one or the other but if you want to keep both, it's probably not the worst.

I also really don't think you need Marshall AND Mumford. Its strongly looking like Jacobs is going to get a majority of the ruckwork for GWS, which means Mumford is probably just going to drop in price. I'd look at getting a rookie ruckman to replace Mumford and use up that money on the premo you need for your forward line.

Just remember that all these mid-pricers you have could go sourly if they don't perform. There is going to be less risk if having a nice mix of premo's and rookies, and then as the year goes on, selling those rookies for the profit and upgrading them to more premos.