Hmm you seem to be worried about committing any sins; in that case you need to go all 'wali' on Allah, I.e. you need to practice this deen 100% like a wali Allah

so I will advice you accordingly
Is your art for business?, in that case it will be ok to put it online and do what's necessary to promote your business even if it means to praise the works of others to gain contacts and interest in yours, However make sure your paintings or the ones you praise do not include faces of animate creatures.
If it's not for business, then it will be s sin to put yours online to 'show off' and hope for praises and likes and praise others' so they do same to you.
You need to just worship Allah 24/7 and make sure whatever you do is halal and to please Allah (swt)
So the answer is, if it's not for business to make money, it will be a sin to show off paintings to get praises from people and to praise theirs just to generate like for your paintings