Well, there really is a need for roll back, new page reviewer, template editor etc. and of course confirmed, Extended confirmed etc..
The Steward and Checkuser groups grant a user access to highly sensitive data such as IP info. Also it is possible for a user to easily set up these groups himself on a wiki he runs if he is determined enough. Checkuser grants access to a user IP and a log of who got IPs for whoever. This right is restricted on english wikipedia (see: https://en.wikipedia.org/wiki/Wikipedia:CheckUser for more info) but a concession has been made for you to run checkuser on your own IP/username. I suggest that if you want to test checkuser you use that facility. All other rights are simply redundant and the entire wikipedia/test wiki user right structure can be replicated on a wiki you can freely host (I personally run http://testwiki.epizy.com/index.php/Special:ListGroupRights where I have a semi wikipedia style user right structure on a free webhost (I refer to my wiki by way of reference only). It is really easy to replicate any wiki if you put enough time and dedication in it. I also get the feeling that we presently have enough Stewards in comparison to the size of the community. All the stewards have been experienced wikimedians both on wikipedia, this test wiki and a variety of others (Void holds the 2nd highest rank on another test wiki, macfan contributes code patches to mediawiki, mbrt was one of the first users to join and has experience on other test wikis while alvaromolina is a sysop on multiple wikimedia wikis, a steward on a beta network that is essentially a wikipedia replica and actively blocks bad IPs via the use of checkuser). Personally, at this moment we have enough stewards for the community and they have all spent a lot of time on this wiki and in management positions on others. Right now you have spent less time on this wiki and have not shown (much) management experience. I therefore (for now) personally don't think you are experienced enough to make such a big proposal at this time and suggest you wait a while and accumulate management experience before re-proposing.