my very first bed quilt was a very large king sized quilt- if you have the (gumption) to make one that big its do-able for a beginner- as for weight- it will be heavy/warm but i don't think it would be unduly so- my king sized quilt has a flannel backing and batting in it- it's pretty heavy- but living in northern michigan that's nice sometimes
i say go for it- and as for 'struggling' it through your machine- you may want to make it in sections- 2 or 3 at least- then sew the sections together- it will be alot less to deal with at once.