Begin the process by determining your overall budget. How much can you afford to spend? You don’t want to start married life in debt.
Another factor is the capacity of your chosen venue. Capacity is determined by Fire Code. You cannot legally exceed that number.
Make your ideal list, including everyone possible. Then pare it down to accommodate the size of your venue and your budget. Plan 2 guests per invitation. If 300 people are invited and everyone attended, you’d be looking at 600 guests. In most cases, about 65% of those invited will attend so your real number is closer to 390. However, if you live in a rural area and have large families close by, that percentage could increase to as much as 80%, or 480 guests. If your venue’s capacity is only 350, you’ll need to trim your guest list accordingly.
Remember, your chosen venue cannot accommodate more than their published capacity. This is set by fire code and determined for life safety reasons.
One more thing, the more guests you invite, the more people you have to feed. Make sure your budget can handle everything, including food and drink. You don’t want to begin married life in debt.