This is a pretty solid choice for the start. Especially when you haven't fully mechanised your army (yet) and field stuff on foot the Avatar can really perform.
Farseers are a no-brainer, they're versatile and very efficient for their points.
I would probably think about buying Eldrad Ulthran next, he's really worth his points - as long as those points are not like 25% of your whole army. In small games he usually is too much of a target and dies too easy in concentrated fire (compared to other expensive
HQs).
I like the Phoenix Lords, but that's just me. Used properly they can really do something, but you'll have to set that up and work in synergy with other units. For a generic list I wouldn't take them. But if I know who I am up against I really like to add a Phoenix Lord for fun. Asurmen can work against Orcs for example. Bladestorm with the
DA unit he is in to reduce an Orc mob and then assault to kill off the rest including the big nasty one. Still a bit expensive. But fun
Autarchs are great if your strategy involves reserve/deep striking/flanking. I haven't tried Yriel so far, cause he is neither fish nor fowl for me.