To start, beware of confusion on the terms "3-pin" and "4-pin".
FANS (their motors) come in two versions: the older ones controlled only by varying voltage use 3 pins connectors, while the newer design uses a 4-pin connector and a different control system. So they are commonly called 3-pin fans and 4-pin fans.
RGB lighting systems also come in two dominant versions. The plain RGB lights use a 4-pin connector, and the more complex Addressable RGB (or ARGB) system uses a 3-pin connector with a different control system. So LIGHTS come in 3-pin and 4-pin systems.
When you buy a fan with lights built into the frame, you really get two devices in one unit - a fan, and a light strip - and each has its own SEPARATE cable and connector. So you can have a 3-pin FAN (motor) with either a 3-pin or a 4-pin LIGHT system built into its frame. Likewise, you can get a 4-pin FAN (motor) with ether type of lighting system in its frame. Of course, you can buy either type of FAN with NO lights in the frame, too.
So, when you say you are buying "3-pin fans" and then want details about how to connect lights, I conclude you may be very confused by it all. You are correct about the LIGHTING headers on your mobo - it has two of the 4-pin plain RGB type plus one of the 3-pin ARGB type, and those are used for the LIGHTING portion (and cable) from any fan that has lights. WHICH header you use depends on the LIGHTING cable from your fans. Now, the ARGB header (3-pin type) says it is limited to a max total load of 3A for all the lights plugged into it. You CAN use "stacked" ARGB Splitters to connect 9 LIGHTING cables from 9 fans to a single header ONLY IF their total load for the LIGHTS only is less than 3 A. How do you know that? You need the specs from the fan maker's website. You have not told us exactly WHICH fans you are talking about, but if you tell us we can help look for the specs. IF it turns out the load is too large, there are ARGB lighting Hubs that can be used to power the lights from the PSU while taking the Control signals from that mobo header, but we don't know yet whether you might need that.
Connection of your fan MOTORS to mobo fan headers is a separate issue. If you need advice on how to do that, ask here. Your mobo has three CHA_FAN headers, so nine fans may be do-able with simple fan Splitters.
Important item to clarify: When you say nine fans, is that solely the case ventilation fans? Are the CPU cooling fan(s) a separate group, or did you include that (them) in the total of 9? Do you have ANY lighting devices in addition to the nine fans?