ST. PETERSBURG — Amid a hub of construction and closed sidewalks, the opening of the new Tom and Mary James Museum of Western and Wildlife Art is months away, but leasing for its prime downtown retail and office space has begun.The museum at 100 Central Ave. is where 400 to 500 pieces of Tom and Mary James' extensive art collection will be on display.The Sembler Co. has begun marketing the ground-floor retail units, while Echelon Real Estate Services is leasing office space on the second floor.Mike Talmadge, executive vice president at Echelon, said the firm already has several prospects for the 20,769 square feet of office space, but added that it is too early to reveal who they are."The occupancy downtown is very tight and there is very little quality space left," Talmadge said. "The James Museum building probably has one of the largest blocks of contiguous office space in downtown St. Petersburg."Echelon is offering the space at a starting rate of $26 per square foot, he said.Steve Althoff, senior vice president of leasing for Sembler, said the company is leasing about 13,000 square feet on the east side of the Central Avenue building and 7,600 square feet on the west side.He said they're looking for an "upscale restaurant" for the western side."On the east side, we are looking for retail and service-type tenants," Althoff said. For example, he said, offices for doctors and lawyers, a spa, an upscale barber shop or hair salon, jewelry store and dress shop.Both retail and office spaces are expected to be occupied when the museum officially opens in early 2018. The James Museum is taking shape on the south side of Central Avenue, across from the One, a major construction project that includes a 41-story condo tower and hotel. The museum has also begun advertising for an executive director.Tom James, chairman of Raymond James Financial — who stepped down last week and will now be known as emeritus chairman — has collected more than 3,000 pieces of art with his wife over the years. Besides being home to a large selection of the couple's works of art, the new museum also will include an American Indian jewelry collection.The 80,000-square-foot James Museum will have more than 30,000 square feet of gallery space. It will feature a 2,500-square-foot, two-story indoor sculpture court with an indoor waterfall. It will also have a 120-seat theater, a 6,000-square-foot museum event space, a catering kitchen, a museum store, a cafe and a high-end restaurant.