Starting Strength Results and ?'s

[TexLacrosse]

These are my results from roughly 11 weeks on the program. I have reset each exercise twice and I'm begin to begin a 5x5 routine in 12 days. (as soon as I get back from the beach for spring break, hellll yeahh. haha). Anyways, I probably wasn't the best candidate for the program because I have been lifting about four years now but it was great. It taught me amazing form and I was very pleased with the results. Check the numbers, let me know what you think and it would be greatly appreciated if you would answer questions below about future programming. Sorry this post is kind of sporadic and unorganized I'm tired as hell.

Age: 17
Height: 6'
Starting Bodyweight: 173
Current BW: 177

Starting 5RMs (pounds):
Squat :275
Bench:195
Standing Military Press:105
Deadlift:275
Rows: 135

Current 5RMs:
Squat: 335
Bench: 225
Standing Military Press: 120
Deadlift: 305
Rows: 195

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Here is what my programming looked like by the end of the program:
Monday - Workout A
Squats - 3x5
Bench - 3x5
Deadlift - 1x5
Dips - 2 x 8-15
GHR - 2 x 12-15
Abs

Wednesday - Workout B
Squats - 3x5
Standing Press - 3x5
Rows - 3x5
Pullups - 2 x 8
Abs

Friday - Workout A
Squats - 3x5
Bench - 3x5
Deadlift - 1x5
Dips - 2 x 8-15
Curls - 2 x 8-12
TriEx - 2 x 8-12
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Questions:

I did this program without a belt, but I just got a belt and am considering using it during my journey through 5x5 for back injury prevention, good idea? will it prevent core strength development? if i do use it how/when should I use it? ( i.e. deadlift and squat? only on final worksets?)

Why do you think my deadlift progressed horribly? (I never missed a deadlift workout)

Is 5x5 a good route?

I am getting my 5x5 info from wildtim's madcow 5x5 post (wont let me post links) and it doesn't say anything about accessory exercises, all it shows is the compound lifts. What kind of accessory work should I be doing and when?

It also doesn't mention cardio... how much and when? ( I run alot in lacrosse already so as of now I typically limit outside running to 30 min twice a week)

Is 10 days off between now and then too much? should I do something in between?

I'm sure ill have more questions but just cant think of them right now.

Thanks ahead of time.

[TexLacrosse]

also what can I do on offdays?