My 150 presently has 4 Monos ranging from 8-14 inches, One Johanna around 9 inches(she's actually the meanest fish in the tank) and a 10 inch Lima shovelnose.
I used to have a spotted shovelnose also but my largest Mono ate it, I'm suprised the Lima hasn't been eaten yet also. There is a fine balance in sizes between Shovelnose and Pbass, sonce one will almost always be tryig to swallow the other.
All the bass went in between April & may at sizes from 6-8 inches, now in September things are starting to get cramped since my wild ones are so much larger than the farm boys (the farm monos were 1.5 inches on January 15th of this year!). The Peas will soon be housed in a 300 (hopefully by end of December)
You can do everything you have talked about, for a while, time is not on your side. Just remember, when you catch the Cichla Flu, you'll be shopping for a bigger tank, so always keep your eyes open.