Best Wishes on your upcoming wedding!
Easy answer: 150. But, we know it’s more complicated than that. There will be friends & relatives who you would certainly want to invite, even if you know they won’t be able to attend (due to travel, health, cost, other plans, etc.). And you would know their situations better than I can guess.
If there are 25 people who you know won’t be able to attend, invite 175.
The less notice you give them, the fewer will be able to attend. If the wedding is 6-12 months away, and you’re sending “Save the Date” notices now, more will be able to attend.
If the 150 limit is set by the local fire department for a building, you certainly can’t go over. If the venue can only set for 150, you can’t go over. Caterers can usually accomodate a couple of extra guests above the final head count you give them (depending on your menu selections).
All the best,