Trying to build a model condition that only shows records the user has read/write access to

I didn’t play with this, but you could create a model based on the account share object. Create your conditions so that only households/activities with the access level you want are queried. This may be the only model you need depending on the level of editing you need to do on the account object. Alternatively, you could create a second model on the account object and set a condition to only display rows that are in the accountshare model.