Hi and welcome!
Good that you are doing your research first!
Indoors piggies are generally more interactive with you, as you get to see more of them. Quite a few members are moving their piggies outside for the summer months when there is no danger of frosts; but they will need to be protected from too much heat, too.
Guinea pigs should never be kept alone; they are very socially interactive group animals.
With boars, you want to make sure that they are character compatible to last past the hormonal months between 4-14 months old; often an age gap helps. Stick to a pair!
http://www.theguineapigforum.co.uk/showthread.php?t=76162
Sows can be pregnant from 4 weeks onwards and can get impregnated by any boar over 3 weeks old, so you need to check that or you may be up for a very steep learning curve that not always has a happy ending.
By far the safest place to get piggies from is a good rescue; any piggies up for adoption are quarantined and vet checked, properly sexed and bonded and guaranteed not pregnant. You will also get advice and support during the settling in period and the whole of the rescue piggies.
If you are in the UK, here is a link to a list of recommended (and vetted) guinea pig rescues of good standard, practice and ethics.
https://maps.google.co.uk/maps/ms?msid=209994852075231951564.0004b8fd9391b4257d8eb&msa=0
For housing ideas, have a look in our housing section through the cage and hutch galleries. The RSPCA minimal space recommendation for 2 guinea pigs is 2x4 ft for two piggies; we recommend 2x5 ft for two boars.
PS: As we have members from all over the world, we would be grateful if you added your country/general area to your details so we can pitch you the appropriate links, advice and recommendations straight away as they can differ quite a bit. You can do so in User CP/edit profile/location. Thanks!