Hello @5329871e
It was my first Chanel buying experience too 
The first visit to the store (Bond St), we sat and waited about 45 mins before someone was free. DH was not impressed! (they log everyone coming in and work down the list).
The Sales Assistant was great, took loads of time with us, showed me lots of different bags. I wasn't quite sure which one to go for then, but the SA gave me his WhatsApp and said just text him when I knew. He was very good on giving me info about how long it might take different styles/sizes/finishes to come into stock and had lots of advice on finishes etc.
A couple of weeks later, I texted to say I'd made a decision, and he was straight on the message and replying and checking stock. I was a bit lucky that the one I wanted, they had in stock, so he saved it for me and I arranged with him to come in later that week.
This time, when I turned up at the store, I said I was here to see the SA and that there was a bag ready for me to pick up. She bumped me straight to the top of the queue and I was seen about 5 mins later. Tried the bag on again, said "yes please!" and that was that! Worth noting that you do need to show ID if you are spending over a certain amount, I think £4k.
So I would say, the initial visit is a bit like hard work, and be prepared for the bag you want not to be available. But after that, it all seemed very straightforward. I don't know if I was lucky with the SA, though! - he was great, and very very helpful.
Don't be nervous about walking into the store - I was a bit, because I am by no means super rich/confident/stylish, but it was actually a really nice experience 