Since this is your first orchid tell us what window it's in and how your
taking care of it. A pot an inch bigger than the root mass would be
good for size wise. Roots growing like weeds is a good sign-your orchid
sounds healthy-I don't know what that medium is but you don't want it in
soil (as in normal houseplants) Orchids loose leaves now and then as
they grow new ones-they'll turn yellow this is normal. Now with the
reusing of old soil, don't do this with orchids I think they can go a
year without repotting but in the mean time their medium breaks down
(decomposes) so use fresh sphagnum moss or orchid mix. Usually when I
buy an orchid I repot it immediately and I always find bad roots-you may
or may not....good luck....don't try seeing a doctor for your orchid
fever once your bitten there's no cure only the relentless drive to
quench your thirst with more, more, more!......Burr