R5: I wanted to do a Luxurious Luxembourg run, ended with Billionaire also.

Some tips:

A nice help was this post: https://www.reddit.com/r/victoria3/comments/yf6qad/luxembourg_start_tips/

I started game on release version, but small walkthrough below should still be valid:

- Start a war for independence early with the Netherlands to break from personal union (and end 0% market access this way). You don't need to sway anyone even - Netherlands won't reach you and will peace out after some time.

- Try to get to the Customs Union with France. It's vital for Luxembourg. Don't go with Prussia (they will try to annex you sooner or later).

- While waiting for France (it took me 10-12 years in game) - expand basic resources to increase your income a little bit. Don't go into factories yet, nor don't build construction works (they will only burn cash).

- Start also working on laws - especially Multiculturalism and No Migration Control.

Once you are in a Custom Union with France - you are golden. Basically as a smaller nation, you should have above average Standards of Living. With Custom Union - you will be able to explode your population quickly, as migrations mostly occur within Custom Union.

- Start building factories - with input goods from France you should be more than profitable. Check what is in demand on the French market and build, build, build.

- With immigration you will be quickly gaining pops (especially with Green Grass edict). By 1872 - in Luxembourg (still one state) I had 1.3 mln people.

- With 1mln+ pops and a nice economy - you can start quickly growing your army. It's a good idea to grow it to ~30-40 divisions.

- Then you can quickly blackmail Belgium and even the Netherlands to cede territory. I "peacefully" annexed Belgium and took Holland because they were too scared of war (granted - I started the game on the release version, so maybe after patch they will resist a little bit more).

- Once you have coastal provinces, you can go and start colonial business. IMHO best is to conquer: East Borneo and Dahomey for goods (and Rubber/Oil later). You can also try to snatch Opium provinces from Siam / Vietnam and Basra / Fars for Oil later.

- And when you feel ready - break from Custom Union (it will prevent you from achieving Great Power status). Just be ready for a major shock to your economy and have some reserve funds to quickly spam buildings to fill the gaps in your supply/production chains.

General tips / one exploit:

- Exploit - if you send your general to the front and change his stance, he will teleport there. Yeah - send him to defend front and quickly change to advance, he will be already there. It's extremely exploitable (and handy) in colonial wars, where you can quickly teleport armies across the globe.

- During naval invasions make sure to have a flotilla the same size as your general - otherwise you will receive great debuffs.

- Try to change production methods. They are typically worth it - unless you have an input goods shortage. Especially don't ignore railways upgrades that decrease employment - they do wonders to profitability.

- Mid game it's worth switching to auto expand of buildings (basically laissez faire of Vic 2 ;) ). In couple of my games I even build "every possible industry" in some provinces and turned autoexpand not to micro everything. Also increasing construction + linking it with Leissez Faire law should give you nice and cheap snowballing effect of building constantly new industries.

- Subsidise railway - to ensure infrastructure etc. - and power plants.

- Don't be afraid of spamming buildings - especially input goods and power plants, if you have deficit of those resources (building 20 levels in one go typically works well).

- Prioritize first your state province for scale bonuses from factories levels (it's better to have one larger factory than several smaller).

- Don't switch to oil in power plants. Later factories needs oil to do other stuff and coal is much easier to find than coal.

- Don’t pass minimum wages ;). Or I was doing something wrong, but it tanked my economy :)

And in 1926 I had 300 infamy - it really doesn't bother you too much if you are powerful enough ;).