The backpacker’s rule of “When in doubt, leave it out” applies in your situation. One of the advantages of staying in one place for a month is that you can figure out the best place to buy anything you really need and YOU WILL be able to buy anything you truly need. I would plan on 7 to 10 days worth of clothes (you’ll still have way more clothes with you than any local you meet owns).

You can store luggage in lockers and “left luggage” rooms at major train stations and airports, but generally the limit is 30 days and it can get very expensive (3 to 5 euros a day). Make sure you fully understand what will happen to your bag (it may only be left in the locker for 1 to 7 days, and then taken somewhere else), the hours of operation for the storage room, etc. Best would be to find a friend where you can leave a bag while you’re traveling. You will probably end up on an intra-Europe flight or two. Cheap airlines usually charge for ALL checked baggage and have a weight limit of 15 kilos (about 30 pounds) and HUGE overweight charges on checked baggage. Some airlines even limit the weight of carry-on items.

Limits on trains are what you can carry since there are no luggage carts and no porters available and you don’t “check” your gear. My rule is what you can carry with one hand free. Try to avoid oversized bags (over 24”) as they will be a problem on some train cars and make you unpopular on any crowded train. On most trains you keep your baggage at and around your seat — preferably on the overhead rack. On some train cars, bags are stowed at one end of the car and there’s only room for carry-on sized items at your seat. If you end up on a commuter train there may be almost no room for anything bigger than a briefcase.