You can use a crossover cable to connect the firewall to the router. This crosses pins 1,2,3, & 6, which is what Ethernet uses.
For the 25 remotes, you can certainly use the same transform set and key (although you may not want to use the same key). If you use dynamic crypto maps, you can have all of the remote sites connect to the central site. You will need to define interesting traffic in the "nat 0" statement if it's a PIX, and also define what traffic should be encrypted.
I would create a separate peer for each remote, defining what traffic gets encrypted.
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
Table of Contents Introduction:This document describes details on how
NAT-T works. Background: ESP encrypts all critical information,
encapsulating the entire inner TCP/UDP datagram within an ESP header.
ESP is an IP protocol in the same sense that TCP an...