I've been using Vivaldi as my main/work browser for the last ~1 year. Tab tiling and tab groups have been absolute game changers for my workflow and curbed my objections departing from the firefox camp.
It used to feel quite slow with too many open tabs when I started using it, and would improve by hibernating them every now and then (which is built-in functionality). It seems to have improved significantly with recent releases, haven't had to hibernate tabs for quite some time now.
Snowplow is also an option. It’s an open-source data collection solution that, unlike GA, gives you full ownership of your event-level data and the freedom to define your own data structures. Not exactly what you’d call ‘lightweight’ but quite a few Snowplow users/customers have come from GA for the level of flexibility and control they can have over their data sets.
Sorry to hear about your trouble. For me the deal-breaker for Revolut when I was looking at my options was that it's not really a bank, while N26 is (which means deposits are protected up to 100k). So I went with them and have no regrets so far.
For example deployd is open source AFAIR; others (like Firebase, Parse) are hosted solutions. But overall they all give you instant CRUD over your data. In your case, their turn-key multi-user capabilities are a bonus.
It used to feel quite slow with too many open tabs when I started using it, and would improve by hibernating them every now and then (which is built-in functionality). It seems to have improved significantly with recent releases, haven't had to hibernate tabs for quite some time now.