You will certainly have issues keeping the planets on target with a manual Dob and effective focal length of 4500mm - my advice would be to invest in a Goto mount

. Achieving accurate focus will be extremely difficult!
Not too sure what you plan to achieve by combining an image without the L filter, note the focus point in the high IR will be significantly different to the visible part and will probably adversely affect the result. I've never seen anyone do this before...
If you haven't seen these before, I'd recommend watching these tutorial videos, they cover everything from the equipment to the software.
http://planetaryimagingtutorials.com/