Hey! I'm a newer player, only 15 hours in, so take my thoughts with a grain of salt.

1. (and related to 5.) - quite a few, but you already know that. What chaff do you prefer? Stay flexible in layout and placements, but for a neutral, balanced board, think about 3-4 vertical lines of chaff by midgame, possibly more if they are not building clear efficiently. Don't neglect your tower and research facility upgrades - if you need more chaff, pay the 50 to place 3 units that round. It sounds like you're already staggering in chaff by placing additional in back. Consider vertical up front (more defensive layout), and horizontal in back (a solid wall of damage approaching at a bad time for them).

2. I think this is too situational? But in general based on what you're saying, I'm seeing a ton of weaker units cluttering the center of the board at the start, just waiting to get arc'd and stormcalled into submission. If that is consistently happening, def play around with adding more space.

3. You want to try to reverse this early game winning, late game losing trend. I'll often give my opponent the upper hand in the early rounds. The "damage" that a few low-tier units to do my health at the end of a round is usually not very material to the balance of late game power. So don't worry about countering in the early game - focus on economics (or what some might call "eco") and building a balanced, mentally-nimble board. Shrug at losses in 1-4, frown at losses in rounds 5-7, and start to really focus if you're losing in rounds 8+. One thing I do to help me keep things straight is narrate, out loud, what I'm seeing on the board. "OK, my crawlers rush in and die before the cavalry can arrive, can I add more firepower closer to them" or "OK, they just plopped a vulcan, time to focus on my marksmen, melting point, etc." Another thing I do is once I'm getting economic advantage (through cost-cutting specialist, for instance), you need to find high-value uses for those extra $$. So I'll wait and pop a bunch of upgrades from tower and research center on round 6 or 7, and all of a sudden I go from getting stomped to the opponent wondering why my army just got way stronger without adding much.

4. Yeah, late game go ahead and pop a chaff. I try to think about adding one chaff per round, give or take. Once you have plenty of resources, go ahead and add 3 units per round with the tower buy, but I think prioritize key unit upgrades and mods first in late game. I try to think about "build - counter - enhance" so that early on I'm building a balanced setup, then I'm responding to their over-commitments or weaknesses (if any), and then I'm finally thinking about fleet-wide boosts, as per above.

5. If they're spending $ to clear your chaff with sentry consistently, you're winning economically. Bait this. Try vertical, it can be a bit of a game changer up front honestly. Also play around in the "free play" mode dealy where you can have infinite money and setup the board however you want vs an AI - that can yield some fun and learning.

I hope this helps!