I trained Xingyiquan for years, currently focus more on Taijiquan, I am no expert, but what do you want to know
Is Xing Yi Quan difficult for me in my 30s which is currently over weight with no martial arts experience.
It's more a case of whether you have a teacher local to you and if they know their stuff , which is difficult to ascertain with no (I)MA experience. Why Xing Yi in particular ? You'll probably find taiji easier to find, basically a competent instructor is more important than the style, whatever the art.
If you have a decent teacher near you, it will be "difficult" at first, in as much as that it is a new skill to learn. But, it should be no harder than any other martial art.
IMO, XingYi is easier for your body than most of the MA systems. For example, you can do 60 XingYi Beng Chuan by only spending the same amount of energy for 20 side kicks or 10 jumping kicks. I can drill 1,000 XingYi Beng Chuan non-stop. I can never do that many reps for any other MA drills.
Speaking as an over 50 guy with arthritic hips.... if you have a good teacher it should be no problem
There is a teacher from China teaching Taiji Quan, Bagua Quan and Xing Yi Quan. I read online that Xing Yi Quan has lesser forms, built up your internal energy and is good for self dence. Hence, I am considering taking up Xing Yi Quan. Any advice?
Xingyiquan, trained right, is good for self-defence, it was at one time, taught to the Chinese military. IMO, of the 3 so called internal styles, it is the quickest to get from theory to application. But this of course depends a lot on the teacher and the amount of time the student puts into it. But most traditional xingyiquan practices start with a lot of stance training; Santi Shi. Also by comparison to Taiji and Bagua, it is not flashy or pretty and the early stages of training can be rather uncomfortable (see stance training)