You can have as many players as you want in your team, there are no limitations apart from economical - each player will be paid wages each week, so excessive number of players will drain your wallet much faster.
There are no player nationality rules or restrictions - f.e. you can have club set in Sweden and have no Swedish players in your squad, you can hire any players you want as long as you can afford them.
New players might need some time to fit into the team, so frequent changes in your squad might not be a great idea.
If you have data analyst among your staff you can use team analysis. It contains bar charts that show you comparison of basics statistics of your team in recent matches: points, field goals, 3-point shots, rebounds, interceptions and blocks. Similar data are available for each player in his details (only with data analyst hired). Access to them will help you spot the weak elements in your lineup comparing to other matches.
FUEL Baskteball simulates basketball competition, in which your team will compete with others in league divisions for the championship title. Each week you will play 3 matches (on Tuesday, Thursday and Saturday), for each you can choose completely different lineup, according to current form and fitness level of your players. Each player is described using 10 skills and 9 character traits, from each match you will get a full statistics for each player, which will make it easier to make further decisions.