Welcome to AA
Read the articles on this forum
here
especially the 2nd article on fishless cycling.
SW takes more time to set up than fw. The axiom is 'nothing good ever happens quickly in sw", so take your time.
Decide now if you want to keep the
cc substrate or switch to a
DSB and if you want to add enough
LR to eliminate the need for the Magnum. Also, start putting together a shopping list of the items you need e.g powerheads, salt, marine testing supplies, a refractometer to check salinity levels, etc.
It's also time to start thinking about whether this is going to be a FOwLR or reef tank.
Spend lot's of time planning now. Come here often to read the articles, postings and to post your questions, thoughts and your plan. The advisors and members will point out the good and bad points in your plan and help you adjust it for success.
Good luck and Happy New Year!
Cmor