You asked several questions and you have a lot of responses here but I am hoping to more specifically answer your questions:
What is common practice or code when running new electrical lines in a home(15 amp/20 amp) in a basement that feed up to the 1st and 2nd floor of a home?
This question is quite vague and I am assuming you are using Type NM cable. The Code compliant practice is to secure them properly and install them in a "neat and workmanlike manner" according to Article 334 of the National Electrical Code. Iggy gave you the section of Article 334 regarding securing and support and some examples of NM cable staples.
Is there a rule on how many wires can be run down the same floor joist overhead? In other words, If I need to run 10 new 15amp/20amp lines, can they bunched together and secured to the floor joist overhead safely, or is there a rule on how many cables can be together?
Short answer: No there is no limit to the number of wires that can be bunched together. EXCEPT if you are passing through a partition that will be sealed or caulked the wires have to be derated (meaning they can not carry as much current).
334.80 Where more than two NM cables containing two or more current-carrying conductors are installed, without maintaining spacing between the cables, through the same opening in wood framing that is to be sealed with thermal insulation, caulk, or sealing foam, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(3)(a) and the provisions of 310.15(A)(2), Exception, shall not apply.
Additionally the cables are normally installed through the joists when the are run perpendicular to the joists unless they larger wires.
334.15(C) In Unfinished Basements and Crawl Spaces. Where cable is run at angles with joists in unfinished basements and crawl spaces, it shall be permissible to secure cables not smaller than two 6 AWG or three 8 AWG conductors directly to the lower edges of the joists.
Lastly you asked:
And what is the rule if these wires need to cross a metal gas line?
There is no "rule" or Code prohibition. NM cable can be run with, or across, gas lines or other metal piping systems.