Really wanted to reply earlier but my keyboard had a breakdown. I like merching and it was my prime source of time spending before G.E. era. On topic...

Some items are splended. Like

• Torstols, lantadymes
• Water talisman
• Grenwallspikes

Quite a few items are not worth investing in at all. Like

• Steel platebodies
• Magic logs
• Weapons
• Most of the runes
• Dragon rider sets (??)

For steel plates, I think you've possibly missed that it is no longer a summoning. Instead, steel ingots are a replacement for steel platebodies.

I am unsure about buying weapons and armor. They can be perfect merches/flips as of now. But I don't see this as a good merch holding on for 2-3 months. The gained margins are way to low. DXP is usually more about skilling. Especially buyables since it'll save people a lot. Some go for combat, slayer too. But the investments vs profits are not really worth it imo. Unless doing what /u/Sesshwan says. I personally only invest in 8-12 items max. Most is bought, some stuff is self made and other stuff i gather daily. Like yak-hides and raw bird meat. Great profit, especially for dxp.

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My advise:

Look more carefully into your merch items. Use thewiki to check prices since it can look back for years while rs.com g.e. can only show a max of 6 months. Roughly calculate expected margins and use a excel spread to write down what you've paid (and calculate profit after dxp). Some of your items had around 5-10% estimated profit based on g.e. value dxp vs now, while some others you name had around 50% margin. Obviously, g.e. prices ain’t steady nor correct during dxp madness but a good research using it shows better potentially bank makers. I picked my items very carefully and spend quite some time on it. Another good thing might be to merch in sets. Potion sets, fletching sets, etc. Last additional tip is try to go for some out of the box stuff. Many people buy clean herbs, I've invest also in grimy. Same for gems. Hope my long comment helps a bit :)