Are you buying new or used? Even the cheapest most basic certified refurbished or brand new MacBook Air using a Core i5 and 4gb of RAM will make easy work of word processing, web browsing, and most applications.
My advice is always get the most RAM and best processor that fits your budget... but even the base model MacBook Air is a capable machine.
I am buying new. I would prefer to have 8GB RAM but the store i'm purchasing it from (Best Buy) only has 8GB RAM for 128GB models. I am buying a 256GB one.
I would not compromise on RAM. Get the most you can as that will help extend system usability and performance for future OS updates, and apps that require more RAM. 8GB RAM will provide a better overall user experience now and in the future.
For what you are mentioning here 4 gigs of Ram is enough.
I'm able to run Logic Pro X on my MBA with 4 gigs of ram. About 60 audio tracks. I didn't buy it for this purpose but it works great. I bought mine for the same tasks you mentioned and it's able to do much more. If you can afford a maxed out machine go for it.