[Dan in Pasadena]

With the size area you're talking about I would not recommend what you propose. You'll do a lot of work to prep and then end up with a lot of weeds.

I would get advise getting an excellent kill with the full strength Roundup - It is about $35 a quart, but that should be more than enough for your area.

Then you can rent a "sod cutter" to remove the dead grass/weeds, do your trench/sprinkler install, lightly scarify and level your existing top soil and put down sod. Instant lawn and the sod acts to kill as a light barrier any possible remaining weed/grass (though I doubt you'd have any). No weeds, no weeding, no waiting for seed.

An option would be to rototill after you get a good kill but leveling and rolling - even a smaller area - is a LOT of work if done properly. When you consider the work you'll be saving and the much better quality of the finished product I would never use seed again unless I were doing a huge area.