As per your suggestions, I have made below arrangements:

R1 to ISP1 over EBGP

R2 to ISP2 over EBGP

R1 to SWH1 over OSPF

R1 to SWH2 over OSPF

R2 to SWH1 over OSPF

R2 to SWH2 over OSPF

For outgoing traffic:

On Routers, I will have default route from each ISP and will redistribute the same in OSPF. SWH1 will have two default routes from both ISPs redistributed via OSPF. Any traffic comming to SWH1 will load balance (per packet) between both ISPs. The same hold true for SWH 2 as well.

For incomming traffic:

I have devided /23 pool into two /24 pools and influnced the BGP decesion using as-path prepend and I don't find any problem in this.

Please correct me if I am wrong.

Again a doubt: My traffic for abc.com is loadbalanced (per packet) between both ISPs using two default routes. But the return path will be from either of ISPs. Will I be able to open webpage?

rgds/bsn

Suggest you avoid per packet load balancing. Just use CEF's per flow load balancing.

How to acheive this and is it scalable for 1000 users accessing internet?

rgds/bsn

On Cisco platforms that support CEF, all you need to do is insure CEF is active and not configured for per-packet load balancing. (This would be done on the OSPF L3 switches that connect to the WAN routes.)

As to scalable for 1,000, that depends on the equipment and the actual traffic load they are making.

PS:

BTW, an issue with spliting your /22, it alone doesn't guarantee equal load balancing unless traffic to/from each /23 is equal.

Other comments:

For outbound, OER/PfR can dynamically load balance. PfR can also dynamically load balance inbound, but that's complex.

Also, other than trying to achieve better load balancing, asymetrically routing shouldn't be a problem (unless it leads to unicast flooding).

Is there any other option OR setup which can be used for load sharing with default routes.

rgds/bsn

OER/PfR will work with a default route.