On this team Toppo is outclassed as a support unit by Honest Admiration Super Saiyan Cabba and The Spirited Golden Warrior Super Saiyan Gohan (Teen), both of which offer Ki in addition to the ATK and DEF boost; on a team so diverse it's important to have some form of Ki support to keep it consistent. The only reason why you would run this unit is to activate [The Invincible Myth of Universe 11] Jiren's most powerful ATK link, Hero of Justice, but SS Gohan (Youth) can do that too while also offering Ki and having more cohesive links overall with the rest of the units on the team. Toppo is not a bad support unit on Super STR, he is a solid choice as a floater if you lack the options I mentioned.
"Universe Survival Saga"
The fact that Toppo does not offer any Ki leaves little to no reason not to use [Greater Mind and Body] Super Saiyan 2 Kale in his place, which is obtainable in-game through the [Tournament of Power] Story Event; they give the same ATK and DEF boost, but SS2 Kale is way more valuable on the team since Jiren offers only 2 Ki with his Leader Skill. Toppo also does not link as well as SS2 Kale with other units on the team like [Limitless Growth] SS2 Caulifla and [Dawning Supernova] SS2 Kefla, both of which would appreciate have at least Super Saiyan active since that's basically the only ATK link they have. Why should you run Toppo on this team? While it's true that Toppo does limit the options since his Passive only affects Super types, it's also true that he links incredibly well with Jiren, the Leader of the team, and that is much more valuable since he is one of the strongest units in the category and you are going to have two of him. Toppo, as a floater, can maximize Jiren's potential with [Super-Dimensional Instinct] Goku (Ultra Instinct -Sign-) on rotation, and he makes it easier for him to Super Attack.
Super ATK
Toppo's Super Attack causes supreme damage and raises Super type allies' ATK by 25% for 1 turn, which is not particularly useful if he is a floater; Toppo will benefit from the 25% ATK boost himself and it will stack if he performs an additional Super Attack.
Leader Skill
A rainbow Leader Skill for Super types is good, but the boost and the Ki is too low; Toppo will probably become a decent Leader when he Dokkan Awakens, but he will still more than likely outclassed by [All or Nothing] SS God SS Vegito, a Free-To-Play unit.
Passive Skill
The support Passive is pretty good, especially since there is still room for improvement. The only problem is that under a 2 Ki Leader Skill, Ki would be very valuable, but when Jiren Dokkan Awakens, giving Ki would be redundant on a team on which every unit shares the same 3 Ki links like in Super Saiyan 3.
Link Skill
Shocking Speed is a good Ki link in general and Tournament of Power makes it easy for Toppo to fit on Universe Survival Saga, but outside of that team there is really not much; Signature Pose is pretty much useless and the same goes for Supreme Warrior. Hero of Justice is the only ATK link Toppo has, it's nice because he is the only unit that can activate it for Jiren aside from SS Gohan (Teen), but there is nothing else, which brings down the value of the unit. Getting Fierce Battle would already be quite good and Warrior Gods would be amazing for a Dokkan Awakening.
Toppo is Jiren's best linking partner, he shares "Shocking Speed" and "Tournament of Power" with him, which would guarantee both of them a Super Attack under a 3 Ki Leader Skill; Toppo also shares "Hero of Justice" with Jiren, a 25% ATK link that would be otherwise difficult to activate for the Leader of the "Universe Survival Saga".
Super Saiyan God Goku and Toppo share only "Shocking Speed" and they don't have any ATK link in common, but Toppo's support Passive will greatly improve Super Saiyan God Goku's ATK due to the fact that he receives his boost upon Super Attack, making it a 134% ATK boost.
Ultimate Gohan and Toppo share "Shocking Speed" and they both give Super type allies a DEF boost for a total of 80% more DEF on rotation; this boost is very valuable on top of Toppo's high natural DEF.
Hidden Potential
While we are still waiting for this unit's Dokkan Awakening, so far the best investment would be Additional and Critical; somewhere around lv.9 Additional and lv.17 Critical is probably the best way to if we think about the fact that Toppo might become a staple unit on rotation with Jiren to put in the first slot. You can invest in Dodge, but, as I said, the unit actually has a pretty high natural DEF and does benefit from his own Passive.
Should I use Elder Kais/Grand Kais?
So far there doesn't seem to be a reason to use Kais on this unit; Toppo is meant to be a support unit, not a damage dealer, and he does not have a farmable Super Attack.