Hi!
The FM birds will require more than 5 watts to get thru all the QRM.
Not at all. In fact, lots of folks make QSOs on their HT and ALH-800 antenna every day. I made 2 yesterday morning with W7JPI and KG7EZ, with just such a setup.
And on 3 different passes today (one AO-51 pass this morning, and two AO-27 passes this afternoon) I made about 13 contacts with a similar setup. Sometimes, on very high passes, I will go to a long duckie like Diamond's RH77CA or SRH77CA instead of the whip, and once in a while even break out a VX-2R and work the FM birds at 1.5W on those antennas. With a dual-band Yagi or log periodic, I have gone to 500mW and (a couple of times) even down to 100mW and still made contacts.
What is ten times more important than your power output is the ability to work full duplex, especially when it's crowded. The 817 and 897 neither will do this, so consider adding a 2nd receiver of just about any sort to work the birds like a pro.
Definitely work on the receive side of the station before transmitting. Since only a few watts - or less - is all you need for the satellite to hear you, work on the receive side of your station so you can hear those low-powered signals coming down to you.
For most of the past 2 months, if I am on the satellites I am using an HT (Icom IC-W32A or IC-T7H) and a long telescoping whip (Maldol AH-510R is my preferred whip, but I also have an AL-800H whip in my HT bag). I could make a few more contacts with a directional antenna instead of the long whip, but having a small bag with everything I need for my FM satellite station is pretty neat.
Good luck, and 73!
Patrick WD9EWK/VA7EWK - Phoenix AZ http://www.wd9ewk.net/