The more patterns you throw into the mix, the more chance you have of loud pattern.
Overo as a name is a total nonsense as it means nothing at all, none of the patterns is in any way genetically linked to one another.
I would go with Mona's suggestion and start with a well marked LWO+ Stallion, whose bloodlines and pattern please
your eye, and then buy some nice mares with as many visual patterns as possible- you can get Splash/Tobiano/ Sabino all rolled into together and have NO chances of Lethal White foals , so long as all you mare test negative I would go for what you like, and then you can't go wrong!!
JFYI I bred my Silver Bay minimal Tobiano stallion to four mares last year, all visually solid, although one carries very, very minimal Splash.
So far I have three very wild Tobiano foals, all Red base (one Red Dun), and one black mare left to go....there is NO rhyme or reason to pattern, and NO guarantees, so I stick to what I like and then I am never disappointed.