If I want to plant companion annual plants (example Okra and sunflowers, tomatoes and basil and pepper...) How far will every plant be from the other in order to obtain a good symbiosis?
My suggestion is to consider the spacing requirements of each variety of plant you'll be growing in a companion plant setting (or any setting, for that matter). The spacing requirements are almost always printed on the seed packet. Space your companion plants so that the plant that requires the most space will have enough room, and plants that require less space have a bit of extra room.
On the other hand, there is no hard and fast rule to determine the spacing requirements of companion plants. Some plants can be grown in the same bed and planted very closely as long as the plants have different growth rates/harvest times. For example, basil and tomato could be planted quite close at a young age as long as you harvest the basil before the tomatoes get too large and shade it out.
If in doubt and if you have enough space, opt for setting plants farther apart than you think they need. Anecdotally, this year I planted my tomatoes way too close together (about 1-2' apart). The result was fairly healthy tomato plants that were extremely difficult for me to harvest from. Next year I plan to plant rows 6' apart minimum. So even if you plant your plants too close and some crowding results, as long as you're still generally within each plants' space requirement, you probably won't experience much in the way of negative effects. Experiment!
For details on pairing tomato and basil, consider this article: https://growherbsgarden.com/growing-basil-and-tomatoes-together/
For more information on the specific companion species and varieties you'd like to grow, I'd advise studying each kind of plant individually and learning about its needs and preferences. Ideally you'll be able to find articles on the specific companion plantings you'd like to attempt, but if not (I found little on okra and sunflowers), you'll be well on your way to determining what is best for your plants, garden, and growing conditions if you study each plant type individually.
If you're able to discover new information through experimentation, maybe come back to this question and post an answer to spread your newfound knowledge. I'm interested to hear how your garden fares.