Major minus is that items do not appear on searches by default, and so you still need some non-store inventory items to attract buyers.
Plusses for me (with the basic eBay store subscription) includes the ability to form a basic style to the listings with logo on the listings and the invoices, and customised search filters of all my items in my eBay store.
Not really sure at present how useful the store inventory format really is with it's limited visibilty in searches and higher final value fees. Some sellers find it very good for sales others not, it really depends on your wares and customer base.
The standard auction and BIN formats appear in the store so it is not compulsory to use the store inventory format.
Regarding eBay fees, some items do not need gallery pictures, I only use them if the appearance is critical to the sell.
Starting items too high costs a fortune in fees, partly because of the insertion fee itself but also the higher the start the slower bidding is likely to start off. So you can lose out by little bidding or worse still no bidding. Ideally you want bidders to think they are getting something cheap with a low start but they fight over it tenaciously and push the price up much higher.
I use the Auctiva store front as well and that does not need gallery pictures, it and the scrolling gallery will use the header picture, so for cheaper items I do not need the gallery fee
Look at other sellers of similar wares to your own and check their completed sales, then have a go for a month and see if it works for you, it may still be free for the first month too !
P.S. I think most people start by buying things then start selling off odds and ends from their house, I did too.