Dear Gayathri, It is enough to keep Lord Balaji's photo or even Guruvayoorappan's photo. They are allthe same. I too do not have photo of Lord Vishnu and used to always keep Lord Balaji's photo. All the best for a successful pooja and in buying your dream house. Om Sri Sai Ram
Tomorrow being Thiruvonam star and also falling on Saturday, we can do the pooja and I am sure our prayers will be answered, being Vishnu's favourite day (saturday).
Today I did the pooja. Today being Panchami and also Thiruvonam I did both the pooja and did Rava Kesari, apple, orange and milk mixed with honey, sugar, elachi for neivedyam. I will try and attach the photos, since I could not do the same.