I've been continuously playing since I posted on your reddit submission. I started playing very actively and have gradually transitioned to less active. I'd usually try to get a milestone before rebirthing if it would take me a couple hours or less playing actively. My builds were usually pretty flexible to get the milestones though I've described what I remember using below. I try to get most of my experience in lower tiers, since it doesn't generally seem worth tiering up except for milestones.
For very active play, I can switch between multiple levels to click each the encounter on the bottom left for all 4 types of divine abiding. This leverages that clicking never has an effort cost, so it can be used to make progress across multiple levels at once. It can be used to make progress on high levels too; whenever phys/mental effort runs out, you can click to restore effort and then click each of the encounters before the effort bar fills and you can still make normal progress. Clicking can also produce floating icons that can be used in the same way. For this build, for skills I'd often focus on click output + click speed, then right view's Karuna to click output, right effort's Karuna +25%, right thought's +2 divine abidings, right view's Metta to others and right effort's Metta +25%. For tools, I usually didn't have any. Dharma wheel is fine to use, but doesn't click fast enough and focuses on click boost over encounter progress.
For passive play, I'd normally maximize skills that give divine abidings and effort recovery. If I'm trying to play passively in tier 2 encounters, then I'd also take Right concentration/mindfullness so that ceiling(total mental energy divided by mental recovery) = ceiling(total physical energy divided by physical recovery), use journal tool to help recovery, and once I have 250+ skill points, maybe take Right Concentration's 100% mental recovery. Dharma wheel tool is only slightly negative due to click boosts, so can be used for milestones that need multiple tools.
For ~2 milestones, I used the mala beads tool, but active play or the above passive build progresses it much faster.
From rebirths, the best use of karma is raising starting skill points (once in level cap after 4-5 levels in that), starting insight, all divine abidings and then whatever else is needed to hit the next karma seed threshold for milestone/path (reshuffling earlier choices if you need more seeds). Last rebirth I took focus: activity to boost divine abidings which seems decent. I kept waiting for skill points per level to be better, but starting skill points just scales too quickly (each level giving +5 to the level to reach before it becomes worse) and I'd only end up with 20-30 more points after reaching the point where I'd want to rebirth again. Observation rewards have a 10 min timer and low chance which makes them not so useful. Idle rewards and encounter exp don't work well for pushing exp which I'll describe below.
Once you can get dharma wheel 2, this build tries to spend as much time reflecting as possible since that's usually the fastest way to get exp. Tier 0, level 0. Tools: all in dharma wheel. Insights: right speech 7 + insights, right action 7 + insights, right effort all insights except Mudita, Right view all insights except Mudita, right thought divine abidings +2 and +4. For remaining skill points, you want to get click output high enough so it always clears the encounter in a single click, then maximize the exp from 10% of Upekkha gained as Exp during Reflection by increasing divine abidings, then put the rest into effort recovery.