Regarding how much and how often - the simple answer as I see it is "the more the better"...
Most authorities recommend that we would all benefit from getting our daily step count up to 10,000 and that would make a great target (although there is nothing to say that you should not do more)...
Get a pedometer and wear it and see what your step count is. I suggest that you wear it for every step of the day and that way it can encourage you to be more active generally in your daily life - not just on the one exercise walk that you may do.
As a rule of thumb - 10,000 steps is roughly about 5 miles.
There does not have to be any sort of upper limit. I set 15,000 steps as the minimum that I shoot for - but Tuesday last week I did 30,249 steps. Tuesday tends to be a big dance day for me...
You could combine walking with your art. Take art things with you and have a far greater choice of subjects to paint or draw. You could end up seeing things while out walking that could inspire you
When I started walking I was very big and very unhealthy. It took me all my time to walk 0.6 miles. I pushed myself to walk further as soon as I felt that I could - and I got stronger, healthier and thinner and pretty soon I was walking quite amazing distances.
I must admit that as far as muscles go - my first step was that I got a fairly light pair of wrist weights and started wearing those for maybe a mile of walking near my home - just swinging my arms as I walked along...
I also took some keep fit and pilates classes where the only weights involved were based on leaning my own weight. My current muscle exercises are all in the keep fit or dance arena.
I know that there is a great exercise section of this forum - and I am sure that there will be postings on more advanced stuff involving weights - and we have forum members with a lot of experience in that whole area.