[Humble Bundle] Newbie's question

Once you've paid the dollar you just need to pay the difference to unlock the higher tiers except in a couple of bundles which have had the option disabled.

All the extra monthly games unlock at the same time which I think is the first Friday of the month usually.

Yes always $1+ for Steam codes. Sometimes they're DRM free to.
If you payed for the $1 tier and want to get the higher tier, the way it used to be (not 100% sure now though) is to go to the page where you got your Steam keys and there was a button that said "Increase your order" or something like that at the top of the page. Just add enough to the $1 already to make it go over the BTA or whatever and should work. If not I'm sure the support would understand

About the monthly, yes all the games get released on the first Friday of the month.

Ignoring Steam sales or not is totally down to luck. If there's a game you really do want that's under a year old, I would say just buy it. Waiting for something to be bundled is a complete raffle.

It shows the average price people have payed for the bundle, just pay $0.01 over that price and you will get all the games and then a week later after the initial reveal of that bundle they add new games to that bundle (Although there was one recently that had no extra games the week after)

Hope this helps :)

Additionally, should I ignore Steam sales from now and just wait for these bundles?

As a rule, everything gets bundled. Certain big publishers [Eg, Valve] never bundle, and certain indie publishers [usually who only have a single game or software that don't feel they can afford to discount that highly] are consistent in not doing so, as well.
Basically everyone else does bundle, no matter how big, small, niche, or well-known they are.

If a game has been bundled several times, you can be fairly sure it'll be bundled again.
Flip side, if it's a game that was bundled years ago from a developer/publisher that hasn't bundled any games since, it's often safe to assume it won't be bundled again any time soon.

If your mindset is 'eh, I'll play whatever' then you can fully ignore sales.
If you have specific games you want to buy, see if they're likely to go into bundles; or, y'know, just pay what you feel comfortable paying [through sales], to support the developers.

There's two rules of thumb, though:
"If you see a game you want in a lower tier of a bundle, you should get it, since you don't know when it'll be that heavily discounted again" and "Sales almost always repeat, or out-do themselves next time around. There's usually no rush there."

So, if your main concern is the money, then yes, wait on bundles. If you have specific games you want to play, however, it's impossible to tell if and when they'll be bundled.
(Also note, DLCs are very often never bundled, or only bundled in 'complete/goty' packs.)

Or mostly the bundles are old games/indies?

They're new, old, AAA, indie; there's not much rhyme or reason to it. Some publishers (big or small) rush to bundle (Daedalic is known for it) while others take 2-3 years to do so (though now it seems to be more "within 1 and a half" for most :P).

For example I had to get DoA5LR from Steam at 50% discount, because there is no way they can be higher.

There's been no indication whatsoever that DoA5LR is remotely likely to ever get bundled.
To the contrary, I don't think Koei has bundled any game yet, so that one was a good call to buy on sale.
Though 50% off?
Nearly all games will eventually reach 75-80% off, with many games preferring to hover at 85% as the lowest discount, and some even going as low as 90% off or more.

tl;dr version, if saving money is your aim, 75% is a good point to aim for (or 80-85% for indie titles).
Of course, there's no guarantees, and you can't ever determine how long it'd take to reach such a discount..

But, again, Koei isn't really known for their sales, and I don't think their titles usually go below the 50-66% off range. (Though in fairness, they don't seem to have any titles predating 2014 available on Steam, so it may just be a matter of waiting long enough.)
So as with any sale, you just have to determine how much you want the game in question.