If you aren’t techy then getting free OS maps is pretty tricky as they don’t want you doing it so it involves a lot of fiddling. I’m not a fan of paying for software and I don’t mind fiddling with stuff but even I was happy to pay for Viewranger. Map packages are pretty cheap (eg £15 for Wales, £40 for Southern England) or you could buy a self select area or I think its about £1.50 for the just the app with no maps, then you can download free maps like opencyclemap and bing, should be fine on an E71. You can do everything on the phone, its dead easy. Increasing the cache is very simple, just setting/maps/map cache size
I just bought my local area in OS maps then a few extra map credits to cover trips, or I use the free maps. If you want that referral code for a few extra free OS maps then email me, nickjbanks(a)hotmail.com