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You need 3 open CCs to drive score even if they all have to be secured. Open Sky issues one with no credit check and I would get in with a CU that has one and is willing to issue you one, also get a share secured loan from a CU that will help with credit mix and show capacity in being able repay installment loans. Do all this as quickly as possible so at your 6 month mark you can ask for an unsecured card or two and then do nothing but use and pay them off every month until you app for your home. You want to only let 1 card report a small balance each month so your Fico is at its highest possible prior to the app for your home.
Your utilization should be approx 9%