23yo with L5/S1 disc prolapse plus L knee lateral meniscus tear

hey all
im a 23yo with L5/S1 disc prolapse plus L knee lateral meniscus tear
been diagnosed with disc prolapse since march 09 off work for 6 months
seen neuro surgeon and decided on conservative tmt, do not want surgery
was getting dull pain in left buttock but has relieved itself
still have persistant pain with left side back, pain relied with some panadeine and nurofen, doctors wont give me any stronger no matter how i complain, need to go to pain clinic
physio has advised me to do core exercises for abs on reformer as well keep active
unable to keep active because of persistant L knee lateral meniscus tear (on and off problem for 24 months, it healed initially but has now flared up)

well is there any other exercises i can do for my back?
went and did pool work for 4 days a week, just stretching and walking back and forth, but cant do anything at the moment, takes me an hour to get out of bed, pain when sitting and not so much walking
i plan to buy a spin bike so i can keep active but now my knee is acting up
plan to get an arthroscopy on my left knee

anyway my question is how long will i be out (time wise) for an arthroscopy to my left knee?
what will i be expecting when ill be recovering, week by week prognosis?
is it too soon to buy a spin bike for 1 helping to keep active for my back (i plan to ride the bike without bending over) and 2 build my strength up with cycling for my knees?
before my injury, i had been riding for a while but will a spin bike help me with my rehab?
are there any exercises i can do other than using the reformer to do core exercises, im also doing the (tuck tummy muscles in, breathe in and out while holding abs) for ten reps?

You can do prone holds etc - but the exercises your doing on the reformer should be fine. Have you had a recent MRI - is it still prolapsed or is it reducing?

Post meniscal arthroscopy you should be moving pretty quickly. Generally returning to sport within 5 weeks. and starting running etc by 2-3 weeks.

If you can use a spin bike without leaning forward then thats ok - but how about a cross trainer? it'll allow you to maintain your lumbar neutral much easier. And definately get into the pool. Thats brilliant exercise.

Good Luck