A write on your entity may need 18 writes, but a get on your entity will cost you only 1 read.
So if you get 5 entries every 30 secondes during one hour, you'll have about 5reads * 120 = 600 reads.
This is in the case you make a get on your 5 entries. (fetching the entry with it's id) If you make a query to fetch them, the cost is "1 read + 1 read per entity retrieved". Wich mean 2 reads per entries. So around 1200 reads in one hour.
For more details informations, here is the documentation for estimating costs.
You can't see on the dashboard how many writes/reads operations an entity need. But I invite you to check appstats for that.