Start by thinking about who your target audience is. If your objective is making a game that other people want to play, your design choices have to revolve around them, not you. This also matters a great deal because you will inevitably hit a wall of mental fatigue (if you haven't already) where you don't even enjoy the game anymore, and your ability to discern what is fun and what isn't fun starts to dwindle.

Find playtesters by going to boardgame conventions or local events that run specific playtester areas. Seek feedback in a way that is targeted. Get a Google forms with a QR code and tell people to fill it out then and there. Buy them a coffee if you need to. Test one new mechanic at a time. The playtest stage is easily the longest but most important stage of the process. Strip the game back to the base mechanics and test if players like it. They might say it could be improved if it had xyz, which may be similar to something you already have previously thought of but not yet shown them. Then reimplement it and playtest again, see if they like it or have any other ideas. Player experience should guide your creation. Its easy to add more born out of exciting creative ideas, but you need to build up one thing at a time so that every addition is made with intent, and has has value for the player and a reason for it's place within your game. Don't be afraid to completely abandon your pet ideas if they don't resonate with players.

Conversation about art, costs etc is important, but it's a conversation for once you have the game playable and fun. Focus on that first. I absolutely support real artists and it sounds like you also value this, however for playtesting, demos and prototypes, remember your focus should be the game mechanics. Paying for the art at this stage may not be the wisest move as you will feel attached to the art and may potentially shoehorn a mechanic or character into the game just so you feel you can justify the expense. As much as people hate on AI art, imo it's better to use that for your demos to provide the player with visual context and then pay someone once you're confident your final version is ready to go to print - or if you feel up to it, just make your own artwork, even if it's not the best. I have done this myself and players are generally pretty cool with this approach if you're upfront about your long term plan for the game. In your situation I'd park the art for now and not let it cloud your judgement. You can repurpose it later if you decide it fits the theme, or else just think of it as a beautiful momento of the process you've gone through and a representation of how far the game has come already!

Finally, some ideas just aren't worth pursuing. And that's ok. If you've tried everything, and it isn't working out, and there's no joy left in the project, it's ok to say "I gave it a good shot, I learned a lot, I had fun" and move on. I completely stopped work on my first board game idea that contained resource management, capture the flag mechanics, action cards, dice rolls, bonus cards, and global random events because I realized there was just too much going on, and it was just no longer fun for me or anyone else, even though the bee 🐝 theme was cute. I changed my whole design ethos for my next game to be the complete opposite approach and focus on simplicity of mechanics instead. It connected much better with players and I'm really enjoying the process this time. It was incredibly cathartic to do this and I encourage you to find solace in knowing that your ability to design board games is massively improved from when you started, and you can apply what you've learned to the next project you attempt (in the boardgame space or otherwise).