Big issue: Now what? The Nets did the hard work of building up a hard-working culture over the past three years and probably arrived at this point — in the playoffs, coming off a competitive, albeit five-game, series — ahead of schedule.Now the Nets have the opportunity to make a leap. This is the next phase of the rebuild, and it can be more difficult than the teardown that takes place in the first phase. Bad decisions in the coming months could reverberate for years and set back the progress the team has made. The Nets have an acre of cap space, and some fans have idly mused about having two max-contract slots, a notion would require the team to make a trade and get rid of point guard D’Angelo Russell. So it’s likely that the team will have one max spot on the docket.The Nets could make a push for a max guy, a star who wants play in New York for a team that is building toward contender-hood. Or the Nets could look to spend on two or three good young players, players who would slide easily into the ethic that coach Kenny Atkinson and general manager Sean Marks have already established.That’s the dilemma. A star player gives the Nets the talent upgrade they need to compete in the East. But there’s some wisdom in holding off on that type of move and continuing to develop what the Nets have established. Signing Jimmy Butler, for example, might seem to be a no-brainer, but what if his addition slows the growth of Spencer Dinwiddie and, especially, Caris LeVert, who has shown star potential?The Nets have put themselves into a position to be a major player in free agency. But just because they can sign a max-contract player does not mean they should.OFFSEASON PREVIEWS:Lakers | Knicks | Bulls | Pelicans |Mavericks | Pacers | Pistons | ThunderFree-agent outlook: The play of Russell this season has altered the Nets’ approach to free agency. He is a restricted free agent and put together a surprising breakout year, averaging 21.1 points and 7.0 assists and earning an All-Star spot.At the outset of the season, conventional wisdom held that the Nets would be happy if Russell played well enough to be a trade candidate at the deadline. He’s not a good defender and struggles to get to the rim.Still, he earned himself a hefty contract this year and the Nets — who have Dinwiddie on a team-friendly contract — just might be willing to pay Russell and keep him in the fold. Otherwise, they risk losing him for no return, and that’s just no way to treat a young asset.But the Nets still need more. Butler has been the name most connected here, mostly because he included Brooklyn on the list of destinations for a trade back in September. LeVert, though, is a cheaper option at small forward and does not come with the team-smashing baggage that Butler has.What Brooklyn really needs is a power forward, though it’s unlikely to find one on the free-agent market. They could bring back both DeMarre Carroll and Ed Davis, which would at least give them some continuity, but would be a missed opportunity to get better.Julius Randle is a young option, though he lacks the defensive toughness this Nets team values. Signing a veteran like Paul Millsap on a short contract — allowing some time for Rodions Kurucs to develop — might wind up being the best option. It’s not a Butler signing, but don’t expect the Nets to use all their cap space just because they can.The young folks: Russell is only 23, which makes him that much more of a must-sign for the Nets. Even if he is trade bait later, he is just too young and too talented to let walk for nothing. Russell is a 6-5 point guard who is an excellent playmaker but has developed into a reliable shooter, too, from the 3-point line and midrange.The Nets have two other players who recently turned 21, both of whom — center Jarrett Allen and Kurucs — were contributors this season. Allen started 80 games this season, averaging 10.9 points and 8.4 rebounds, shooting 59.0 percent from the field. He has a limited offensive repertoire, though he has developed a hook shot that still needs work. But he is a good defensive center who figures to grow into his role.Kurucs showed tremendous potential over the course of the season, a 6-9 forward with a 7-2 wingspan who can shoot from the perimeter and defend multiple positions. He wore down as the season progressed, but better conditioning and a year or two of development should make him a starting-quality big man and a steal of last year’s draft, when he fell to No. 40.Brooklyn didn’t see a lot of rookie scoring wing Dzanan Musa, who played in only nine games. But he averaged 19.5 points, 6.4 rebounds and 3.6 assists in 36 G-League games, at 19 years old, and he should be a rotation player in the coming years.This June will also present an unfamiliar prospect for fans at Barclays Center — when the draft comes along, the Nets will have their own pick in its rightful spot (No. 17). As a bonus, the Nets also have the Nuggets’ pick (27th), their reward for taking on Kenneth Faried. It’s a young group that will continue building with youth. NBA PLAYOFFS 2019:Full schedule | Picks from first round to FinalsWait till next year: There’s a lot to be excited about in Brooklyn, even if the Nets fail to land a top-shelf free agent. The team’s top players are all in their early or mid-20s, and there is more youth being developed on the roster.They survived a spate of injuries and an 8-18 start to finish 34-22 and earn a playoff spot. The young players will improve, and there will be the chance to build in both the draft and free agency. It’s been a rough three years, but the Nets are finally back on track.