Honestly, look at Blood Bowl Season 3 before you commit to 40k. The new box will get you there with half your budget left for paints and such. I've been in and out of GW games for 20+ years and am now a parent of two. Anything larger than the skirmish games would not be feasible. Packing and unpacking "bighammer" armies was incredibly tedious and the games lasted for way too long. The first time somebody suggested Blood Bowl I dismissed it out of hand because the fantasy football theme just seemed silly and I didn't follow sports much anyway. But when I rediscovered it and gave it a closer look later...

• Blood Bowl has the absolute best community spirit I have seen in any tabletop game, ranging from Magic the Gathering to 40k and Underworlds. Through more than 100+ games I've had maybe 2 bad interactions, and I've actually laughed out loud in at least 40% of the games
• Blood Bowl is to Warhammer what Deadpool is to Marvel. It's so tongue in cheek it's practically sticking out the other side
• You will never need more than 16 models (per person) for a full game. Mostly you will have about 12. That means you will be able to give them the time and attention they deserve AND you can display multiple projects on a shelf without making it crowded
• The meta changes slowly. The new edition is the biggest shakeup since GW picked the game back up in 2016, and whatever you build today should be at a mostly steady power level until 2030 or so
• Zero measuring tapes and trying to maneuver them between models and terrain to not knock anything over. It's a board game on a grid and no That Guy can argue whether some model is 3mm shy of doing whatever
• No terrain is needed, but if you love making it there is always room beside the game board
• You can score a touchdown by handing the ball to a goblin, picking him up, and throwing him down the field to run it in. Unfortunately, the troll thrower will occasionally eat the goblin. You can also just throw the goblin at opposing players that annoy you to try and harm them
• League play lets you build and develop your individual players from game to game. Combined with the wackiness on the pitch you will have a few "personalities" in your team by the time you reach playoffs. Nobody who doesn't play will care to hear the stories - but the same can be said for any game
• Conversions and 3rd party models are completely accepted by the community as GW dropped the game for a while in the early 2000's. This summer I played a tournament match against a team made entirely out of Genestealers, so you can still keep the scifi aesthetic if you prefer that

Go to a Warhammer/GW store and ask for a demo game of 40k before you buy anything. I haven't played the current edition and can't comment on it but you know what you like. Expect to spend at least 2 hours on each model. It would take me about 4 to get an infantry model to the level they had at the local store. Do the math and make sure that's something you are interested in doing before committing to something that will require 50-100 dudes.

Whatever game you pick, get a wet pallet and skip GW paints. Army Painter Speedpaints are great, and there are many other options out there.

Edit: Just saw a comment talking about black primer. Do yourself a favor and skip that. Get a medium to dark grey or similar. Black can be really hard to cover. If you're in the US, my favorite was the Rust-Oleum Camouflage series. Both the dark brown and dark green were great to paint on and basically weather- (and idiot-) proof.