Always going bust to set over set?

[rodders133]

Ok, I was playing online 20NLHE full ring last night. I had $25. I limped in early pos with 44. 5 players saw an unraised flop of 4c 5d jd. I didnt like the flushing board or straight draw possibilities and bet the pot.
There were 2 folds, a min raise and a call. I went all in and both players called. One was on a flush draw and the other had pocket 5`s, which took the pot and stacked me.

Questions;

1. Given the above scenario, did I play this hand correctly. If not what should I have done differently?

2. I can remember quite a few occasions where I have gone bust holding an underset, but only once where I have had the overset to someone elses underset and bust them. Is this mainly due to limping in with small pairs?, should I be folding maybe 66 and below even to no raise, as obviously the higher the pair you see a flop with the less chance there is of running into an overset, or in the long run would I make more $ with these small sets busting overpairs etc.

3. Starting hands in general; At the moment my starting hand requirements are quite standard. I always thought I was quite tight, but now I`m not so sure. I have had Pokeroffice for a few weeks now and I am starting to see my level of `tightness` compared to other players. I am maybe seeing 20-23% flops, where others are seeing 10-15% (not all, but some). I understand at this level it should be fairly tight abc poker.

So what hands am I playing that I shouldnt be.....

I will limp in any pos with any pp in unraised pot
I will limp in any pos with KJs, KTs, QJs, TJs
I will limp in late pos with Axs
I will limp in early with AJ, AQ, AT
I will raise any pp TT and above, AK, and AQ in lp,

Any feedback would be much appreciated