All of those are limited.
Unless you want 1/day things, which i don't, then you don't get the same effect.
IMO: the biggest advantage (and difference) of the warlord is that he's martial. Which (generally) means he's unlimited.
I know that's kinda the D&D dogma, that you can swing a sword all day (because no rules for fatigue, and we're forgetting things swing back).
Some, probably a fairly small minority, of what the Warlord does might be swinging a sword in this particular way or that, that's as likely to work as any other attack, every time.
Most of the rest is more dramatic, situational, taxing (not necessarily for the Warlord himself), and/or less repeatable.
That can be heavily abstracted as n/encounter, n/rest, n/day, n/level, n/ever or n/whatever - none which would not really be in keeping 5e's greater emphasis on concept (not that that stopped them from giving just about everybody some n/rest deal or other).
*(and healing can't be at-will).
Less abstractly, when a Warlord inspires an ally to do something /more/ than he normally would, that ally is making an extraordinary effort, comparable to the kind of thing only fighters typically do - and you can't do that all day, even in the absence of rules for your sword-arm getting tired. For hp recovery, that can mean triggering HD, 4e-ish though that might feel, and that's pretty reasonable. HD are the hardest to renew resource in the game, recovering only half your HD per long rest (and there are variants to further reduce that) - even 9th level spells aren't so hard to recover! - so that'd be a pretty hard limitation, right there.
For inspiring anything else, you could, again, abstract it down to 1/rest/ally - since most non-fighters aren't normally up for that kinda thing, maybe even 1/long rest. Which is kinda blah, but reasonable. It also means typically only 3-5 times a day, with that not going up particularly with level (parties typically get higher level, not higher membership as the game progresses), so it starts out nice compared to 3 spells/day, but rapidly becomes /more/ limited than spells. In particular, not being able to pile healing spells on a PC who gets particularly picked on in a given battle could be terribly limiting.
There are probably ways around that (the alternative, when faced with a more-limited ability is to make it /more/ powerful). Rather than a hard 1/day, you could have a CON save with increasing DC (and at least some allies' CON saves will improve with level, making it more accessible at higher level), or a penalty like exhaustion or something. Or, a high-level ally might go more times/day, if the warlord was of comparable level. Quite a few possibilities to get the level of limitation into the right ballpark.
Then there's tactics. An obvious idea would be that you can't, for instance, spring the same 'surprise attack' on the same enemy, or even an enemy who saw you do it last time. That does abstract down to 1/encounter, rather neatly, but, again, n/x - blah - plus, what about the ever-popular recurring villain? This one could also go to a saving throw, but instead of an ally /making/ a save so they can benefit from being Inspired again, the enemy makes an INT save to figure out your cunning tactics and negate them (in whole or in part, depending - possibly even making things worse).
Then there's flexibility. What a given Warlord can do with Inspiration is probably pretty set, it depends on his talents and his relationship with his allies. It might eve be ally-by-ally. You can inspire Barg barbarian to attack ferociously (damage buff) with no problem, it's harder to inspire him before battle (temp hps) - that kind of thing - what kind of mechanic that might be IDK, could just be the player of the ally having some input into what kind of buff he wants to use on his character, could be presenting that player with a choice of how to use your inspiration.
Tactics, OTOH, are the kind of thing you have to mix up all the time. You'd want to change up tactics as fast as you could dream them up and drill allies to execute them. Really crazy high-level ones might even get out and become well-known, rendering them virtually worthless beyond an initial use...
