One aspect of retaining and energizing existing members that seemed to be glossed over (see question #2) is that Christians who get involved in whole book Bible studies (doesn't matter much whether OT or NT) will grow their faith and depend more on it. Those with stronger faith are a lot likely to leave or drop out per some superfluous nit or perceived slight. They won't get riled up about carpet colors or the style of new chairs for a meeting room.

The two basic paths to growth & retention are: Focus on the Bible, solid preaching, adult education focused on Bible book studies, solid hymns that feature good music and sound theology, prayer and devout worship. OR the focus can be on making people feel good, offering promises of wealth and happiness that Jesus did not and would not offer. Offering a litany of blame-free misquotes of the Bible, happy songs that imply that "I found Jesus", trying to convince people that "all is well" and that the Christian life is easy may boost attendance for a while but it will not solve anyone's problems for long. These counterfeit outfits often fail to acknowledge that happiness is a temporary balm based on human whims and that joy is a gift of God that lasts.

The churches that rely on devaluation or dilution of the Gospel (because a lot of the Gospel is hard to hear) will fail because they do not offer what Jesus has always offered. His Church is founded on what has been revealed to us in the Bible and prayer. When, as is likely, the seas get rougher in the future days our task is to stand fast with our Lord, don't bow to or knuckle under satan's current rendition of what life should be. We have the Bible and 24/7 access to our Divine Triune God via prayer. That's all we need.

Remember what Jesus said about the Church at Laodicea!