Thing you should note while selecting plants for your garden.
(a)As you said gardening is your hobby, you will be knowing about many plants especially flowering plants. Hence go for the ones you like the best.
(b)Second thing you have to consider is the climate prevailing in your region.
(c)Thirdly always go for rare flowers and plants that are not seen in the neighboring places, this creates and attraction towards your garden.
(d)Choose flowering plants that suits the color of your gate, house and wall. Overall the garden in front of the house should give a pleasing look to any eyes.
(e)Include medicinal plants which has small colorful flowers too. This gives a good look as well as can be used in times of emergency.
With the help of seeds can we grow plants with flowers.
Yes, you get to buy the seeds of many flowering plants from the market. You get small flowered plants in a pot too. Visit any flower melas or get seeds from any shopping malls.
As you said you have varieties of Rose in your garden, now you can go for Orchids, Dalia, try Tulips as well. Why don't you try growing vegetable plants, you can use the vegetables in your kitchen as well.
"Do not give up, things might not favour you always"