At 50nl and below, I'd recommend opening from UTG in a 9-handed game with something like AQs+, AQo+, 66+. At UTG+1, I'd add AJs and KQs. At UTG+2, I'd add AJo and KQo and ATs. I'm pretty sure this gives you a wide enough of a range in EP that nits and set-miners aren't likely to be able to exploit.

If you aren't getting 3-bet much and having to play with bad SPRs, raising to 5x with all of your opening range from the first three positions instead of 4x might help a considerable amount, especially considering that Full Tilt players (from what I have seen) tend to buy in short more often. Maybe it's something to experiment with at 25nl and 50nl, I only did this at 10nl in EP to thin the field just a little to limit schooling post-flop.

Also if you aren't getting 3-bet much at all, you could add 55-22 to your EP ranges if you so desire, but it's something to keep an eye on for profitability. At the very least, it will get you playing more hands against presumably worse players.

As far as telling the difference between TPTK and a set on a board like 863 against your set, I suggest you take notes on how players play sets and what players are really aggressive with low TPTK hands, the goal being to start to develop the intuition to have a feel for when unknowns have each.