Freelance riding instructor here. First of all welcome to the wonderful world of horses!
I'm presuming since you mention you are complete beginner, you ride at a riding school on their horses, so below advice is completely based on that assumption :)
Before buying riding skirts / long coats, it is worth speaking to your riding school to see what their policy is about clothing, just to make sure what you are planning is allowed... Also what works now might be redundant when it's 20+ degrees outside (over trousers, full chaps & such)
Loose & long clothing in general, unless specifically designed for riding, might be uncomfortable when you start moving to faster paces. Long coats & tops have tendency of getting stuck in saddle & hindering riders ability to rise to the trot for example. They'll also hide your body from the instructor, which means it will be more difficult for them to advice on correct riding form & help you to progress (I've used baggy jumper many a times when feeling slightly tired, and not wanting to be told of about sloughing
)
Riding skirt - tinyurl.com/dxehzkji
Top - Baggy is not quite as bad if the back part of the jumper / jacket is flat, and does not cover riders hips / bottom too much (or is taken in on the waste and then flares out). So for example this would be ok tinyurl.com/4h4ty4du Also gillets are your friends here.
Half chaps - Yes for these, not just to cover your legs, but to give nice lower leg stability! They do need to be correctly fitted though, not overly loose.
Breeches - Little Bit Racey (ignore the name, it refers to racing, not style!) breeches are jockey style but designed for ladies hips. Loose at hips, tapered at the bottom. Go a size up for extra looseness. I dont race, but love these. (pcracewear.ie/collections/paul-carberry-a-little-bit-racey-collection)
Hijab - You probably know this already, but Adidas does sports hijabs, which might be more comfortable under hat when you start moving to faster work. Also bear in mind that hat still needs to be correctly fitted with hijab, and not just whacked on top of it loosely. If not properly fitted it'll do more damage than good should you fall off and hit your head.
Enjoy your new hobby, and hope you'll find the riding outfit which works perfectly for you!