Darth Plagueis was a Muun who trained Palpatine.
Darth Plagueis was also a Sith alchemist (unorthodox scientist) and he experimented on Shmi - perhaps without her knowledge somehow - and genetically engineered Anakin to be the perfect Sith - high midichlorian count and a trustworthy face with which he could be a popular ruler.
In some manner, things were manipulated so that Shmi and Anakin would be hidden away as slaves on a backward world in the Outer Rim.
Plageuis' intent might have been for Anakin to grow up and kill Palpatine, when Palpatine was of no further use to Plagueis.
Palpatine might have known about Anakin and caused him to be "lost."
Palpatine personally killed Plageuis in his sleep (maybe - or he had some assassin (Darth Maul?) do it for him.\
Sith Lords are supposed to be exceptionally hard on their apprentices and make them hate them to fuel their Dark Side. Eventually, the Apprentice becomes the Master by killing the latter.
Palpatine might have hated aliens because Plageuis was an alien (a Muun like San Hill of the Banking Clan).
However, Palpatine USED aliens - like Darth Maul - when it suited him, so Maul was a tattooed freak the public would fear and never submit to, ensuring that Maul could never rule the galaxy. On the contrary, Palpatine engineered his being ELECTED Emperor He was popular and well-liked when he took full control of the Empire.
He likely wanted an Apprentice that could do the same. I'm sure he knew Dooku as a Jedi. He also knew that Dooky was heir to a fortune from his homeworld of Null. Dooku could raise the funds to finance the Separatist Movement and get it going - like paying for battle droids as well as the Clone Army's beginning (Lama Su and Jango Fett's fees).
Dooky likely killed Syfo Dias to cover up the authorization of the Clone Army. Remember, it was begun being engineered when the events of TPM were going on at the same time!
Darth Maul was just a tool, like Dooku was using Asajj Ventress.
Dooku was also very popular - with the Separatists - and he could also lead the galaxy if Palpatine failed. Ventress could not, just as Maul could not.
No - there were not armies of Sith as had been tried and failed before. But Dark Siders were persuaded to join all along, with the promise of becoming the Sith Lord.
These Dark Siders were impressionable YOUNG Force Users, like Maul or Ventress.
I don't think Darth Maul was the real Sith Apprentice.
The Jedi Order was misled to believe so.
Thus when Dooku was revealed to be a known Sith Lord, he was thought to be the Master - perhaps Maul's master - while Palpatine was never suspected.
Anakin's loyalty to Palpatine became useful when Palpatine needed to get rid of Dooku - and had Anakin not undergone such physical tragedy (on Mustafar) - he would have been the perfect Sith Lord to reign as the 2nd Sith Emperor (and retain his popularity as a war hero, too).
However, the expanded universe also has Palpatine messing around with Sith Alchemy trying to "cheat death," by use of his own clones (Dark Empire comics). It's debatable whether or not that actually worked (transferring Palpatine's spiritual Force into the clone), but Joruus C'Boath from HTTE was a clone of Jorus C'Boath - though not the exact same person.
Had Anakin survived and stayed allied to the Sith, there might have been a power struggle between him (Darth Vader) and Palpatine's new clone.
However, the whole plan revolved around Palpatine ruling in absolute, unchallenged power, and perhaps cheating death to continue to do so.