I finished first run with 5/50 medusa, 5/50 blade, gr, 5/50 iceman, and 5/50 domino, no single 5* I had then, it was some time ago, September last year or so, now should be even easier more champs, wider possibilities.. Just try it, you'll find answer yourself, good luck. 😀
It can be done. I got to 5.3 with Maxed 4*s and a R3 5*. I definitely could've gotten to where I am now (5.4.6) with the R3 5* but just naturally leveled him along the way.
Comments
You should be fine if you do uncollected.
If you want advice for champs, my team was..
5* Sabretooth
4* R5 Blade (Duped)
4* R5 GR
4* R5 Medusa
4* R5 SW/LC (Duped)
Sabretooth was my MVP for fights where I needed to take down enemies quickly/boss fights.
Blade was great for damage/regen and the niche fights he counters really well. Void especially..
GR is AMAZING at sustainability with his regen (If you can handle long fights).
Medusa is the tech killer, and also really well against champs that need to be armor broken (Howard the *Cluck*, IMIW, etc..
SW was for buff heavy champs/ Hype, and to save my main hitters from dying.
LC is just a nice safe champ to have if duped (Bleed immune/indestructible). Bleed immune either way though.
Hopefully that helps you if you have any of them.