Sharing of DSL-line via WLAN - comments?

We are 3 persons planning to share a DSL connection via WLAN.
Later on expanding with more participants will be considered.

Before we proceed ordering the neccessary equipment we need a skilled
confirmation that our setup looks sound.
We are considering Linksys because of possibility for external antenna
and Tx power adjustment, and because these units suits our budget
well..


Description (see sketch below):

User 1:
Currently has a wired network consisting an ISDN router, switch and 3
PCs.
To this address the DSL line will be ordered, and splitter and
ADSL-modem will be located in his office in building 1.
(Ordering SDSL instead of ADSL might be actual, there will then be
used a dedicated pair and no splitter).
Our ISP will give us one fixed IP address.
Our plan is to install a broadband router after the DSL-modem and
connect user 1's router/switch to it (at the same time connection to
ISDN-router will be removed).

From the router CAT5 wil be installed via open air (stripsed to a wire
or something) to building 2 where the WAP11 AP and 12 dB omni will be
mounted.
The antenna must be mounted here to give line of site to the remote
users.

User 2 and 3:
Connects to the AP via WET11 wireless bridge and 15 dB yagi antenna,
and distributes further in their houses via WRT54G wireless AP/router
or equal.


Points that need to be sorted out:

-The distance from the router in building 1 to the AP in building 2 is
abt. 70-80 meters, possibly up to 100m in worst case.
I have been warned against using TP without galvanic isolation between
different buildings because of potential risk of equipment damage due
to earth potentials. The buildings are on the same transformator but
not the same distribution board.
Is Power over Ethernet the thing here? Is out-of-the box equipment
delivering 5V/1A available so we can feed the line with 12 or 24V from
building 1?
Or shall we just move on supplying the AP from the mains in building 2
and eventually do something to the problem if it arises? A new AP
probably costs less than a PoE solution.

-Is there any point in investing in outdoor CAT5? Normal indoor CAT5
is almost free, might be better to use one of these and change it
after 4-5 year if it is damaged?

-We assume that a router is needed immediately after the DSL-modem for
routing to the different clients and that we need another router at
each user's house for routing from the different LANs to the top-level
router. Does this mean that all packets each direction will be NATed
twice? Will this have any impact on throughput and ping-times at rates
of 1-2 Mbps?

-We are considering IP telephony from a national company (Telio) but
do not want to end up in a situation where we are short of upload
causing decreased phone call quality, for instance when sharing a
2048/512 line.
Can individual ports be prioritized at the routers/switches? If yes,
and if we have done so in our houses, will we have the ability to give
IP telephony priority all the way through the top-level-router?

-Apart from this, does the architecture look reasonable?

We appreciate any comments/suggestions for modifications.


Sketch:

.................................................. ....................
Site 1 Building 1


------ ------ ------
| | | | | |
| PC | | PC | | PC |
| | | | | |
------ ------ ------
| | |
-----------------------------
| --- To be cut
----------- | ------------- ----------
| | v | Zyxel | | |
| Switch |--/--| Prestige 100|----| NT-1 |
| | | ISDN Router | | |
----------- ------------- ----------
Existing network | |
. . . . . . . . . |. . . . . . . . . . . . . . . . . .| . . . . . .
Planned | |
add-on ----------- |
| | |
| Router | |
| | |
----------- |
| |
add-on ----------- ---------- ---------- ISDN
| Broadband | | ADSL | | | Line
| Router |-----| Modem |-------| Splitter |------
| | | | | |
----------- ---------- ----------
|
|
| 70-80m
| CAT5
|
|
-----------
Site 1 | Linksys |
Building 2 | WAP11 |
| WL AP |
-----------
|
|
O 12 dB Omni
/ \
/ \
/ \
/ \
/ \
1 km / \ 1.2 km
/ \
/ \
........../...................\.............................. .........
| . |
O <--15 dB Yagi--> O
Site 2 | . | Site 3
----------- . -----------
| Linksys | . | Linksys |
| WET11 | . | WET11 |
| WL Bridge | . | WL Bridge |
----------- . -----------
| . |
-------------- . --------------
| Linksys | . | Linksys |
| WRT54G | . | WRT54G |
| WL AP/router | . | WL AP/router |
-------------- . --------------