Definitely I would plan on using rebar and burying it deep to anchor the railway ties or whatever you would choose. I like the look or the railway ties so that's what I would go with but beware you will have to replace them over time because they will degrade.
I'd be raising the ground rather than digging in it adding compost and some clay to your sandy soil. And definitely plan it so that you have at least 18 inches on each level to put your feet so that you can weed
with ease. That makes a total width of 3 1/2 feet if you have a two foot planting area on each terrace. I made mine to narrow and when I went to try and weed
from an upper level where I had a walkway I had a bad case of vertigo. Not at all fun for me. I had to watch the weeds
take over the second level because I couldn't get to it. Another consideration is if you have a tiller that you plan to use. How much space do you need to operate it safely?
Depending on how it rains in your area you also might be concerned with errosion control. Since you will be taking up whatever groundcover that currently keeps the soil in place you will have to consider ways to hold your soil in place especially if you have heavy rains during the year.
The addition of the compost and clay will help somewhat and the terracing but I would still consider a winter cover crop and possible a heavy mulch during the growing
season if there is an errosion problem.
Congratulation on the new house and garden.