first thing first, noting that most of your animals are rescue pets, i sugest that you turn your tarantula and your new fish into rescue pets too.
if you need a specialized trainer pls PM me, i have the highest certifications
second thing, tarantula ROCK ... there you go girl ... high 5
third thing, you want your cycle process cut in half, take your filter sponge, get it in a bag of water and ask the LFS
(local fish store/shop) to put it together with theyr own filters. after 2-3 days go back and bring it back to your tank
SETBACK: you will also bring back all the diseases that they have in theyr tanks, but i guess that if you will buy fish from them it won't matter that much
do not forget, if the bacteria looses water contact for more then a couple of minutes it dies. (that ofc means complete water contact)