The Manfrotto 3001 series is a good starter tripod for lightweight gear such as you describe. I recommend getting a full length tripod for scenics. Try to get one that will go to full height (eye level) without using a lot of center post. It is always frustrating to have to stoop, kneel, squat, etc. when shooting and it makes for an uncomfortable situation when in tall bushes! This tripod can be shortened at will and will also shoot close to ground level, a real advantage when working macros.
This style tripod is not that heavy, just bulky. You will eventually come to see the difference in your pictures in terms of sharpness and composition as opposed to shooting without one. Handheld is fun, but I always have a nagging feeling that my pictures are going to be unacceptably soft.
Get a quick release model. You'll be glad you did. It is always good to have a tripod handy for holding a remote flash or the inevitable group photo.
Get a ball head. You'll always want one otherwise. I have both of Manfrotto's pistol grip heads and I still want a ball head!
You will need to be careful when shooting with the D50 and 70-300 on a tripod. There can be specific shutter speed ranges where the entire set up will vibrate and blur shots. I believe this to be the case from 1/15 to 1 second in general, but there are people that have actually studied and documented this phenomenon. I sometimes dampen the lens with a heavy cloth or jacket or even my hand. This works suprisingly well. You will find out what works best for you. It will be interesting what effect the new VR lens will have in this regard.
I would rather use a bean bag than a table top tripod. I believe they are easier to store, less prone to damage, easier to set up, and they double as a neck pillow! YMMV.