yeah this is an example of a batch file I use to load up my steam, basically it find the steam location from the registry (if it can find it), asks which username I want to load up with and then loads steam with that username. Much like yourself, I got help in creating the barebones of it but refined it through experience as well as trial and error.
@echo off
@for /f "tokens=2*" %%a in ('reg query "HKCU\software\valve\steam" /v "steamexe"') do set "steamdir=%%b"
@rem echo %steamdir%
@if not defined steamdir (
@echo.
@echo.
@echo steam cannot be found, this batch file will now exit
@pause
@exit
)
@echo 1. username1
@echo 2. username2
@echo 3. Exit
@echo.
@rem set /P uname=Select which username you would like to login with
@choice /c 123 /n /m "Select User to use"
@if errorlevel 1 set user=username1
@if errorlevel 2 set user=username2
@if errorlevel 3 exit
@start "Steam" "%steamdir%" -login %user% <password>
@rem pause
you can also use "goto" statemants combined with line markers
goto nextline
:nextline