Leo is a pretty state of the art tank. The two main upgrades needed are a better idler system and metal suspension arms. Several vendors have them, including etoarmour.com, whose computer is in Krimea and warehouse is in central USA. There are also various cosmetic upgrades available including metal replacements for some of the more exposed plastic parts such as steps and mirror brackets. When in doubt over the quality of a particular part, do ask, if need be in a PM on this system.
I have not built a Leo personally, but from what I have read patience and attention to detail is needed. There are several mods some of the builders have made, includine a hinged front plate and modifying the compartment hinge over the DMD to open, giving access to the electronics selection board. Just remember to plan and think ahead during the build, as you should on any build.
Who here can provide photos of the modified turret hatch for the electronics and hinged front plate? Sticks in my mind that doll house hinges were used for that project.