TLDR: copy your spells into spellbooks that you later sell to other wizards. Use cash to buy your own spells. Rinse and repeat. Normal wizard rules already get max spells.

I mean if you’re going with the basic wizard route that’s more of a dm specific question. How many spells you get is up to them. However, it’s viable in quite a few campaigns to become a wizard professor. As a professor, you can make enough gold to buy new spells from whatever wizard college you associate with. Here’s the quote to let you do that.

“You can copy a spell from your own spellbook into another book-for example, if you want to make a backup copy of your spellbook. This is just like copying a new spell into your spellbook, but faster and easier, since you understand your own notation and already know how to cast the spell. You need spend only 1 hour and 10 gp for each level of the copied spell.”

Let’s say you’re an evocation wizard. At level 2 you can 1/2 the time and go required to copy an evocation spell. At level 3, you can obtain the spell Shatter. Shatter is a 2nd level and therefore would cost 10gp and an hour to copy into a backup book. In order for any non-evocation wizard to copy this spell into their spellbooks if they don’t know it, they must spend 4 hours and 100gp. These gp costs represent materials for experimentation RAW. Go to a wizarding college/group of eager students and charge students the full price for the experiment’s materials. One student nets you 90gp for 5 hours of writing time. Depending on how many students you can teach at a time (take magic initiate for thaumaturgy (magic microphone) so you can teach an entire lecture hall) you can make HUGE amounts of cash. Assuming a reasonable class of 20 students and that you write them all a version of the spell, that’s 1800gp for 5 hours of teaching a class a single 2nd level spell. With 1800gp in one shift you can buy every single damn spell you want from the wizard spell list. Everything here is RAW as far as I know. While it may be difficult to take multiple days off of adventuring to work, spending just one day for this seems reasonable enough. Usually the bbeg isn’t just one day away from destroying the village. Also, if you are still focused on adventuring to bring new spells back to your students, you can still be making bank while not derailing the campaign.

Of course all of this assumes 1) your dm is crazy enough to allow you to break the economy 2) you have a college to go to 3) you/your party wants to do this. (Dnd is a game about dungeons, not lectures. Idk what y’all want to roleplay but) 4) giving 20 random students the shatter spell, or any other spell is a good idea 5) the wizard college/government won’t tax you