I opted to keep all of the blades a awakened around so that I can have all of their battle and field skills at my disposal and engage the ones that have the skills I need to open a chest, open a sealed door, open an alternate path, unlock a new area, complete a side quest, etc. The more blades you have, the more likely they'll have the skills you need.

As for raising town development:
Spend money, talk to the townspeople, and complete merc and side missions when they appear.

The cutscene with Klaus during the middle of the Final Boss (which made me completely lose my shit) up until the ending of the game just made me have a fanboy's hope for the plot of Xenoblade Chronicles 3.

Spoiler Tag added ~ CGI

Thanks Rol.

Also, can non-main player characters do level 4 specials? (As in, when used with ZL and ZR)

Really getting into this game now. I'm putting together a quick video on its PQ, which should be ready in around a week.

It depends, check their affinity charts, see if they pick up useful field skills or maybe battle skills (frankly I rarely care about those) before releasing them. If you already have one with a similar element or tool set I say release them and get the boosters. If you are lucky or play the game long enough, you will get stronger blades down the road or find a set that works best for you in terms battles and field skills although most of the necessary field ones are usually attached to rare blades, other mundane ones, (botany, element mastery, etc) that you may need higher levels on are good to have at level 3 on common ones.

Does anyone know a very effective way to change the weather, arf? Changing the time like in previous games don't seem to work for me, arf :/

Only keep common blades that have 3 field skills. That way they can finish merc missions faster. Finishing affinity charts for commons gives you WP and even Overdrive Protocols (4 star only for OP).

Oh, also try to keep any Blitz Ball Commons that have a Luck modifier. If you can get the Luck item from the unique boss in Uraya and two Blitz Ball characters with Luck modifying weapon chips you can get a ton of luck. It makes opening blades a lot less RNG. Open blades with Nia first, until you get two more healers with her. Use Trush/Compassion boosters to up the odds of getting unique healer blades. 

Finally, never open blades with Rex, and always give Rex the item pouch upgrades. Trust me on these. You'll see what I mean once you reach chapter seven. 

Why the item pouch upgrades to him? Or at least why more than 2. I assume there is no reason to have more than 3 pouches per character. You know, put in each blades favorite item and call it a day. Or maybe 4 I guess, to also give Rex his favorite item.

How many bags are there? I have used one on Rex so far. I have at least one more I have not used.

Rex can equip any blade once you reach chapter ten. Pouches max out at three. Throw 30 items of the same type liked into a single bag x3, and make sure they are items that refill every 20 minutes. Between items with doubleheart effects you should average 60 affinity per blade every twenty minutes with refills. 

Ah, so the bag thing is just to get the affinity quicker to all the blades.

No reason to wait 20 minutes if that is your goal though, just click again. You can feed them nonstop if you want to raise affinity quick. Purchase cheap items that they like and just click away.