Well, I haven't tried playing as the Irish in 1.8 - however I have taken a few Native American tribes to the extreme in North America. As they share the same difficulties, namely a permanent 50% autonomy cap on all provinces, I can report on that...
Production and trade are the keys to success in North America. Gulf of St. Lawrence is the primary target, and should be the end node. This has tremendous amounts of fur producing provinces. Combined with trade companies (buildings) and the typical +trade buildings, this trade zone can generate enough wealth to become a world power. Chesapeake is secondary, and a good feeder to Gulf of St. Lawrence. It has a fair number of tobacco producing provinces, which aren't as lucrative as fur, but can generate very good income. If you can take the bulk of the Caribbean, and divert this trade to Chesapeake - you'll be making tremendous profits, as most of the trade from South America flows through this node.
With 60% of Gulf of St. Lawrence, 100% of Hudson Bay, 100% of Chesapeake Bay, 100% of Mississippi, 100% of Rio Grande, and 100% of Ohio locked up, I was able to generate 250 ducats a month in just production and trade (they were typically split evenly). This was as Chickasaw. I imagine a Western colonial power might be able to do better.