Takes no longer than most other Prestige classes to get to the good part, and actually a bit shorter time is spent than most.I like the idea but its way too long and too much of a commitment. This conversion would take half of a character's pre-epic levels. Mythic examples, I can think of, even lichdom accomplish this is a much shorter time.
You can become a construct by 14th level. The only way I know of one becoming a Lich through a class is by taking 20 levels in Dread Necromancer.
I guess if your DM allows you could possibly become a Lich by 11th level, but I don't know of many that would allow a sudden +4 jump in LA.
How does gaining levels in any non-fighter based class give you better combat skills? Through experience and improving yourself and broadening your horizons. No different for this fellow.Honestly I can't imagine how morphing into an animated object gives you better combat skills.
Or if you mean the Spirit of the Thing ability, doesn't really help your combat skills, but imagine being able to suddenly inhabit a trebuchet or some other siege weapon. Just start rolling over things.