Hi Hannah,
Welcome to The Tortoise Table and congratulations on getting your little Hermanns! It's an exciting time, and it sounds like you've done a good amount of research already, which is great. First of all, in case you don't have one already, here's a link to a care sheet for Hermanns, which might answer some of your questions:
https://www.tortoise-protection-group.o ... 014New.pdf
The amount you feed tortoises is actually quite important, as if they are fed too much (or if fed the wrong type of food) they can grow too quickly, their shells become deformed, and they can develop metabolic bone disease). There are several really rough guidelines for feeding --- all they can eat in 20 minutes, once a day; enough leaves and flowers, etc. to make a little jacket or blanket to cover their shell once a day, etc.), but the best way, really is to keep accurate records of growth. We have an Observations Records Booklet on our website which you can either download and print out for free, or buy for £2.00, and that is a good way to keep all your records in one place. Weighing weekly or fortnightly is fine, and it's good to weigh under roughly the same circumstances -- just before or after a bath, just after a poo (it's amazing how much they can lose in just having a poo!), etc.) if you can, but the main thing you are looking for is slow growth of an average of 1g - 3g per month. That is just an average and some months he will gain more and some less, but it's a target to aim for.
With a little one like yours, I would bathe every other day (or even every day if it is hot), in a container that he can't see out of (an old washing up bowl works well), and in water that comes just up to where his top shell meets his bottom shell (or his chin), for about 15 - 20 minutes. The water should be nice and warm (the temperature that you would bathe a baby in), and you might have to replace some of it with warm water to keep it warm the whole time he is in there. I have one of those bendy desk lamps that I just train on mine and the heat from that keeps it pretty warm the whole time.
I won't rattle on any longer, and please come back with any more questions you have (and I'm sure you'll have lots). Just one last question from me though. What sort of indoor enclosure are you getting for him. If anyone has told you or sold you a vivarium (wood and glass type thing that is great for lizards and snakes, etc.), please don't get one of those for a tortoise -- they are very bad environments for tortoises and what you want is an open box-type arrangement, called a tortoise table. If you've already bought a vivarium let me know and we can advise you on how to return it and get your money back.
Also, what kind of substrate are you going to have? The most natural and best substrate for tortoises is a mixture of sterilised topsoil and children's playsand (it most approximates the substrate they would have in the wild).
Anyway, you probably know all this already, so I'll just sign off here and hope that you will post photos of him/her when he/she arrives (we never tire of looking at photos of tortoises!)
Nina