Upgrading Tank Questions

i will be upgrading from a 75g to a 180g in the next couple weeks. I picked up the tank used and have pieced together the rest of the equipment that i need, but i have a few questions.

1. i currently have 1 1/2 - 2 inch sand bed in my 75. its about 16 months old and gets vacuumed when i do water changes. (there was about 6 months were i didnt vacuum it) Im looking to do the same depth sandbed in my new tank and wanted to know if i should just replace all the sand, or add to existing sand to make up the difference. If i add to it, im sure i can get away with not using live sand. Thoughts?

2. I currently have about 120 pounds of LR that has been in my tank since the beginning. I may add a couple pieces, but dont plan on adding much rock at all. In using that much establish LR, even if i replace the sand bed, will my tank still go through all the initial cycle uglies?

3. I plan on using about 100-120 gallons of water that has been in my system for a couple days at least, and the rest will be new water. Any issues with this. would using this much "current" water, help prevent new tank cycling?