Here's what I did. This is only my experience and everyone's different, so take it for what it's worth.
I started by going to a local pinball league. Learned what I liked in machines and made some connections. I was able to affirm that I truly wanted a pinball machine
Bought a stern wild fire solid state game for $200. Enjoyed and fixed that game. Sold that and used the money to buy a comet. Got it working and cut my teeth on an amateur restoration. Sold that and used the money plus my pinball connections to buy a judge Dredd. Enjoyed that for a long while and reached the wizard mode several times. I was looking for something with more depth, so I made an ad that I was looking to trade that plus cash towards a deeper pin. I got lucky and got a twilight zone.
Played that and beat it several times so I traded that towards two dmd games. I wanted to get two games to fill out the gameroom I was building. Traded those pins around a few times to get other games I wanted, sometimes adding a few dollars to help with the trade. Eventually I had worked my way up to potc and jy. Used some bonus money from work to buy an ebd that needed work. After fixing that I was able to trade ebd and potc and get a metallica premium.
I had also met two local friends with great collections and I was fortunate enough to play sometimes. That connection turned in to me selling him the met. Premium and him finding me a great deal on a lotr. I had sat on the cash until I found a great deal, because deals do come along pretty often if you can drive.
Used the rest of the money from selling met. To get a jp to go along with the jy and Lotr. I also worked out a deal with the local friend to store his Congo here while he paid me for the metallica. That only came about because I had reached out and made a friend and used clever thinking to sell him the game and store the Congo. I did all this slowly and financially responsibly so that I was never in a precarious position money wise.
So my advice to you through my experience would be to find a way to get a vehicle that can haul a pin so that you can get those deals when they come up. Find some local friends or a league so you can make connections and determine what you like, all while enjoying some pinball. Don't be afraid of a project, pinside is helpful and sometimes working on a pin is very satisfying. Enjoy the pin you do have and set goals for yourself if you find yourself getting bored with it. List it eventually but wait for a good offer before selling or trading. If you sell, wait and use the money to get better pins when deals come up. Don't buy the hype that others sell here, some of the a list games you may not actually enjoy that much and you can usually find them at arcades anyway.