Currently not, but I expect some to be free again in December, so feel free to check back then.
I'm pretty sure Makuta can more or less do that already since they can directly control Kraata. Might as well expand this power to work on everyone he chooses - only works on beings in sight, though.
Wouldn't make sense, I think. It's not like the Makuta needed a spy in Metru Nui prior to Teridax being assigned to that region. Aside from that there are already a couple Makuta whose job it was - amongst other things - to patrol the Matoran Universe and report stuff or help out amongst other things. Your Makuta could be one of these, I guess. However, if he also is a scientist I'm not sure if that adds up that well.
Actually big groups of Rahkshi are a rather new phenomenon since Makuta have only been able to easily create Kraata since their evolution about 40,000 years ago. But sure, he can focus on researching Kraata/Rahkshi. There were two Makut awho did that already, however - although they both died fairly early. Ormen crippled himself by creating too many Kraata and Anjan's Rahkshi turned berserk.
Maybe read some of the information in this topic - mainly the timeline. Which post that is you can find somewhere in teh first post.
Are you talking about Shadow Leeches? Because a Tridax pod is just the container in which they are carried. I'm not perfectly sure on this, but I think I remember that it was mentioned somewhere that Shadow Leeches can't transform into a Rahkshi-like form. Besides teh Shadow Leeches are a very, very recent development. Your Makuta has to die at the latest around teh time of their first successfull creation.
So yeah, check back in December if you want to participate - doesn't mean you can't already start building, though.
Rules in post 1
All Makuta are currently assigned