First of all, make sure you check their sexes yourself. We do see missexing mistakes from pet shops and breeders and you do just want to be certain you have three sows.
The type of bedding you use is a personal choice - there is no best type of bedding, it’s only the best for you if it is practical and manageable for you. There are pros and cons to each type of bedding.
Fleece can only be used indoors though, it doesn’t work outside as it doesn’t always dry properly if the air is damp (even in summer) and it can draw moisture from the air.
Outside hutches need to be filled with a disposable bedding and hay.
It’s a good idea to line the hutch with something waterproof to protect the wood such as Lino, plastic sheeting etc and then the bedding on top.
Mine live in my shed year round so are bedded on either snowflake softchip or megazorb, all topped with lots of hay. If my piggies have to come indoors due to either being too cold or too hot outside then I do sometimes use fleece so as to not have loads of bits of bedding getting around my house. However I don’t particularly like the fleece - I don’t like the extra washing, having to change it every few days and I don’t like having to get the hay off of it.
Other people would find using disposable bedding tedious, trying to dispose of it (not all councils will take it), constant need to make sure you have enough in stock etc
These are our general bedding guide and fleece guide to help you
Bedding For Guinea Pigs - Overview
This is our fleece guide
A Detailed Guide For Fleece Bedding
Also ensure that the indoor cage and hutch both measure 180x60cm/6ft (or a 5 grid by 2 grid c&c cage) - that is the necessary size for three sows
In terms of them going outside into a hutch. Do you mean:
1. just for summer use during the day but that they will live indoors year round (they will never be out in a hutch at night)
2. live outside day and night in the summer months but live indoors during colder months (which will be October until around May)
3. Live outside year round
It’s just the way you go about it and acclimate them is a timing and temperature thing.
If 1, then it’s warm enough now that they can go into a hutch during the day now. Once day time temperatures start to drop come autumn they won’t be able to go out. So if you are saying you want them to be bigger before going out then depending on when you feel that is, you might miss the opportunity for them to go out this year if daytime temperatures start to drop before you feel they’re big enough. Typically you’re looking at around October being the last of the outdoor time.
If 2 (or 3), then while it’s ok during the day, and actually it should be ok at night at this time of year, given the summer are having it depends on what is happening with night temperatures in your area. It should generally be warm enough at night but it might not be. It was 11 degrees here overnight lately - my piggies are used to it but piggies who are only used to being indoors might find outdoors at night a bit too cold. Normally you acclimate them over many weeks starting around May time. They go out during the day but come in at night for a few weeks and then are able to stay out at night as well once they’re used to it and nights are over 15 degrees. Given where we are in the year there isn’t really much time and as I say with nights potentially being on the chilly side for piggies who may only have been indoors until now.
If 3, that would probably be best to wait until next year now. I would personally them indoors until next spring and then start to acclimate them during next late spring/early summer. There isn’t enough time to really acclimate them before autumn gets here and it gets colder.
If are most comfortable between 18 and 22 degrees. Below 15 is too cold and above 25 too hot for outside time.
For any grass time, piggies who are not used to fresh grass in their diet, cannot just be put on the grass. Their access to it needs to be built up slowly (each year) so as to get their tummies used to it. If your piggies have been put on grass by during their first 7 weeks of life, then that is ok. Otherwise, it’s best to start by picking handfuls of grass to give them in their cage, increasing the amounts they have as the weeks go by, and if in spring time, until the weather is nice enough that they can go out into a run for a short time. Then starting building up the minutes in the run as the weeks go by until they can be on the lawn for a few hours each day.
Normally I start picking around February, and they get their first 15-20 minutes on the grass around April.
This applies every year after a winter without access to grass. Rich fast growing grass on unprepared tummies is a bloat risk.
Feeding Grass And Preparing Your Piggies For Lawn Time
I have also added a link to our new owner guides which you may find helpful. They cover things such as the settling them in, appropriate feeding, and the importance of the routine weekly weight checks
New Owners' Essential Information and Practical Tips Starter Collection
Ps - I have changed the title of your thread so that it helps explain the kind of information you are looking for.
want my girlies to be comfy.
only the best will do… I say now the piggies have nearly emptied my bank and are getting more than my children 
