Don't forget the compounding effects of PoS if you reinvest the proceeds into buying more tickets. The income is actually exponential (look up examples for compounding interest). This will have a huge impact on returns for PoS over the long term as PoW does not do this. Again though, the effects of increasing ticket prices will affect this in the same way that difficulty increases affect PoW and there will be diminishing returns at some point in the future.
This is the command to enable staking forever (until price is 1000 at least): Code: dcrwallet.exe -u YourUserName -P YourPassword --enablestakemining --ticketmaxprice=1000 Got in also while prices were very low and tickets were 2 DCR each. All my DCR get sent back to the pool to buy tickets at whatever price, I figure it will even out later. At first, I started to build a 6 GPU mining rig, but decided to purchase as many DCR as I could and send them to my PoS wallet. When the DCR seems reasonably low, I purchase some more and send them to the stake wallet. I'm still mining with my single GPU and send that to the stake wallet also. Slowly buying parts for my new rig but that has taken second place to making sure the DCR stake wallet gets fed while the DCR prices are still low. Staking is very important right now for those without the pre-built GPU rigs.
Your numbers sound right, I computed the odds earlier using the same equation. You can see a histogram of time to being chosen here from a simulation with ticketpoolsize=81920, or double what mainnet is using. https://forum.decred.org/threads/is-pos-working.531/page-2#post-8980 It approximates a Poisson distribution with lambda<1.