Advertising.marketting - you will need to spend a lot of time or money or both doing a lot of this, with one off type jobs like gutters its always going to be a constant effort unlike windows when it will be an effort for a few years then you can stop all advertising if you want to. Not that it cant be done.
My opinion, i would always look to start a business that was recurring, repeatable, like window cleaning.
I would definately get a window cleaning round up first, gives you a reliable income and a good platform to offer gutters or any other services you like to your customer base. Then go from there. Of course if you are determined just to do gutters then go for it but you will need to put systems in place to get repeat work, reviews, adwords, facebbok, leaflets, website, email marketting, offers and follow ups will be par for the course. You might find you spend more time looking for work than doing the work.