If I seal all the vents for winter but would like to open them during summer for ventilation, is this possible/ recommended?
To ensure getting enough air during summer best approach is to:
Open it up - The easiest and most cost-effective way to ventilate your home is to open it up when the outside temperature is comfortable. Cool down your home in summer by opening doors and windows at opposite sides of your house.
Plan for cross-ventilation - When building or renovating, plan for cross-ventilation from front to back, and between each side of the house. During hot summer days, cross-ventilation will allow you to take advantage of the cooling southerly breezes of early evening.