I guess the most obvious answer would be to not skip t1
A lot of people seem to favor going t2 rather than one for the luchs and while it can also be a very good option, bear in mind that this will severely delay your medium tanks which already come out much later than other factions. Furthermore it will make you quite reliant on medkits which will cost a lot of munitions in the long run.
My advice would be that you should not necessarily go t2 by default, but consider your options as you see your opponents opening. Also there is no shame in backteching to t1 later in the game if you become in need of indirect fire.
Unless you can catch an enemy mortar, the lieg is basically your only option for real indirect fire as OKW.
I think he's talking about Ostheer Mechanised Assault doctrine.
First rule of Mechanised Assault is to know what the doctrine provides that you can rely on without tech. Going only for Assault Grenadiers is a poor choice, so it's always worth building tier 1 for three Grens, possibly a mortar if need be. Assgrens are a unit that will complement a strategy, not dominate it, so if you're on a very urban map they can help, but don't expect them to do too well if you try spamming them.
Usually, Mechanised Assault players will go for tier 1 for baseline infantry, then tier 2 for paks and other light vehicles, and complement it with the pgren halftrack if needed or wait for Stug Es.
With the Tiger being 13cps, you'll struggle to just sit out and wait for it with your Stug Es. I'd always recommend building your tier three tech for more robust Stug Gs and the occasional P4. The Tiger call in will be expected, so don't be surprised if an enemy is prepared to deal with it. Your strategy will vary depending on what map you choose, and it's entirely possible that you decide going all the way to tier 4 for a panzerwerfer is better, or get one after your tiger.
But I must stress, don't skip tier one, because Mechanised Assault is very weak if you rely only on the call ins.