Question #1... the "Freelander" sporrans and the "Buzz Kidder" Rob Roy (3 tassle) versions are BOTH equally nice when dressing-up, or dressing-down. I own multiples of both and wear them 99% of the time. Both are affordable, and both are quite cavernous in their storage capacity.

Quesiton #2... I have made kilts like you're explaining, with "Whistle Holders", beer can holders, pockets, or whatever. YES... it is possible (and very simple) to do. The look, however, is a little strange at first. It has to be done VERY precisely, or else the tartan lines won't match-up and it looks like dog "stuff" when you're moving. The key is to have it done on a kilt that has the hips sewn-down. If it's done on a "free-swinging" kilt, it just looks aweful! That's the main reason that it's done on solids.

On a tartan kilt, you would be better served to get the hidden pockets (like jeans) added, and a rear inner pocket like on AmeriKilts. That way, you have storage without interrupting the flow of the pattern.

Would I personally want to see pockets on an authentic "tank"? NEVER That's like putting $20 plastic hub caps on a Lamborghini Countach!!!